diff --git a/integration-tests-definitions/todo-lists.yaml b/integration-tests-definitions/todo-lists.yaml
index d58aa57a5..b629c73d5 100644
--- a/integration-tests-definitions/todo-lists.yaml
+++ b/integration-tests-definitions/todo-lists.yaml
@@ -10,13 +10,17 @@ paths:
         schema:
           type: string
           format: date-time
-      - name: status
+      - name: statuses
         in: query
         schema:
-          type: string
-          enum:
-            - incomplete
-            - complete
+          $ref: '#/components/schemas/Statuses'
+      - name: tags
+        in: query
+        schema:
+          type: array
+          items:
+            type:
+              string
     get:
       operationId: getTodoLists
       responses:
@@ -174,7 +178,13 @@ components:
         updated:
           type: string
           format: date-time
-
+    Statuses:
+      type: array
+      items:
+        type: string
+        enum:
+          - incomplete
+          - complete
   parameters:
     listId:
       name: listId
diff --git a/integration-tests/typescript-angular/src/generated/todo-lists.yaml/client.service.ts b/integration-tests/typescript-angular/src/generated/todo-lists.yaml/client.service.ts
index b2b626c6f..c17911ee6 100644
--- a/integration-tests/typescript-angular/src/generated/todo-lists.yaml/client.service.ts
+++ b/integration-tests/typescript-angular/src/generated/todo-lists.yaml/client.service.ts
@@ -2,7 +2,12 @@
 /* tslint:disable */
 /* eslint-disable */
 
-import { t_CreateUpdateTodoList, t_Error, t_TodoList } from "./models"
+import {
+  t_CreateUpdateTodoList,
+  t_Error,
+  t_Statuses,
+  t_TodoList,
+} from "./models"
 import { HttpClient, HttpParams, HttpResponse } from "@angular/common/http"
 import { Injectable } from "@angular/core"
 import { Observable } from "rxjs"
@@ -89,14 +94,16 @@ export class ApiClient {
   getTodoLists(
     p: {
       created?: string
-      status?: "incomplete" | "complete"
+      statuses?: t_Statuses
+      tags?: string[]
     } = {},
   ): Observable<
     (HttpResponse<t_TodoList[]> & { status: 200 }) | HttpResponse<unknown>
   > {
     const params = this._queryParams({
       created: p["created"],
-      status: p["status"],
+      statuses: p["statuses"],
+      tags: p["tags"],
     })
 
     return this.httpClient.request<any>("GET", this.config.basePath + `/list`, {
diff --git a/integration-tests/typescript-angular/src/generated/todo-lists.yaml/models.ts b/integration-tests/typescript-angular/src/generated/todo-lists.yaml/models.ts
index 28740557b..ba4801458 100644
--- a/integration-tests/typescript-angular/src/generated/todo-lists.yaml/models.ts
+++ b/integration-tests/typescript-angular/src/generated/todo-lists.yaml/models.ts
@@ -11,6 +11,8 @@ export type t_CreateUpdateTodoList = {
   name: string
 }
 
+export type t_Statuses = ("incomplete" | "complete")[]
+
 export type t_TodoList = {
   created: string
   id: string
diff --git a/integration-tests/typescript-axios/src/generated/todo-lists.yaml/client.ts b/integration-tests/typescript-axios/src/generated/todo-lists.yaml/client.ts
index 4633a7ab2..fd4708d27 100644
--- a/integration-tests/typescript-axios/src/generated/todo-lists.yaml/client.ts
+++ b/integration-tests/typescript-axios/src/generated/todo-lists.yaml/client.ts
@@ -2,7 +2,7 @@
 /* tslint:disable */
 /* eslint-disable */
 
-import { t_CreateUpdateTodoList, t_TodoList } from "./models"
+import { t_CreateUpdateTodoList, t_Statuses, t_TodoList } from "./models"
 import {
   AbstractAxiosClient,
   AbstractAxiosConfig,
@@ -17,13 +17,18 @@ export class ApiClient extends AbstractAxiosClient {
   async getTodoLists(
     p: {
       created?: string
-      status?: "incomplete" | "complete"
+      statuses?: t_Statuses
+      tags?: string[]
     } = {},
     timeout?: number,
     opts?: AxiosRequestConfig,
   ): Promise<AxiosResponse<t_TodoList[]>> {
     const url = `/list`
-    const query = this._query({ created: p["created"], status: p["status"] })
+    const query = this._query({
+      created: p["created"],
+      statuses: p["statuses"],
+      tags: p["tags"],
+    })
 
     return this._request({
       url: url + query,
diff --git a/integration-tests/typescript-axios/src/generated/todo-lists.yaml/models.ts b/integration-tests/typescript-axios/src/generated/todo-lists.yaml/models.ts
index 28740557b..ba4801458 100644
--- a/integration-tests/typescript-axios/src/generated/todo-lists.yaml/models.ts
+++ b/integration-tests/typescript-axios/src/generated/todo-lists.yaml/models.ts
@@ -11,6 +11,8 @@ export type t_CreateUpdateTodoList = {
   name: string
 }
 
+export type t_Statuses = ("incomplete" | "complete")[]
+
 export type t_TodoList = {
   created: string
   id: string
diff --git a/integration-tests/typescript-fetch/src/generated/todo-lists.yaml/client.ts b/integration-tests/typescript-fetch/src/generated/todo-lists.yaml/client.ts
index 260b1600c..6b64a8e34 100644
--- a/integration-tests/typescript-fetch/src/generated/todo-lists.yaml/client.ts
+++ b/integration-tests/typescript-fetch/src/generated/todo-lists.yaml/client.ts
@@ -2,7 +2,12 @@
 /* tslint:disable */
 /* eslint-disable */
 
-import { t_CreateUpdateTodoList, t_Error, t_TodoList } from "./models"
+import {
+  t_CreateUpdateTodoList,
+  t_Error,
+  t_Statuses,
+  t_TodoList,
+} from "./models"
 import {
   AbstractFetchClient,
   AbstractFetchClientConfig,
@@ -23,13 +28,18 @@ export class ApiClient extends AbstractFetchClient {
   async getTodoLists(
     p: {
       created?: string
-      status?: "incomplete" | "complete"
+      statuses?: t_Statuses
+      tags?: string[]
     } = {},
     timeout?: number,
     opts?: RequestInit,
   ): Promise<TypedFetchResponse<Res<200, t_TodoList[]>>> {
     const url = this.basePath + `/list`
-    const query = this._query({ created: p["created"], status: p["status"] })
+    const query = this._query({
+      created: p["created"],
+      statuses: p["statuses"],
+      tags: p["tags"],
+    })
 
     return this._fetch(url + query, { method: "GET", ...(opts ?? {}) }, timeout)
   }
diff --git a/integration-tests/typescript-fetch/src/generated/todo-lists.yaml/models.ts b/integration-tests/typescript-fetch/src/generated/todo-lists.yaml/models.ts
index 28740557b..ba4801458 100644
--- a/integration-tests/typescript-fetch/src/generated/todo-lists.yaml/models.ts
+++ b/integration-tests/typescript-fetch/src/generated/todo-lists.yaml/models.ts
@@ -11,6 +11,8 @@ export type t_CreateUpdateTodoList = {
   name: string
 }
 
+export type t_Statuses = ("incomplete" | "complete")[]
+
 export type t_TodoList = {
   created: string
   id: string
diff --git a/integration-tests/typescript-koa/src/generated/api.github.com.yaml/generated.ts b/integration-tests/typescript-koa/src/generated/api.github.com.yaml/generated.ts
index f03cc9e9c..eb02dda87 100644
--- a/integration-tests/typescript-koa/src/generated/api.github.com.yaml/generated.ts
+++ b/integration-tests/typescript-koa/src/generated/api.github.com.yaml/generated.ts
@@ -34473,7 +34473,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const migrationsListForOrgQuerySchema = z.object({
     per_page: z.coerce.number().optional(),
     page: z.coerce.number().optional(),
-    exclude: z.array(z.enum(["repositories"])).optional(),
+    exclude: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.enum(["repositories"])),
+      )
+      .optional(),
   })
 
   const migrationsListForOrgResponseValidator = responseValidationFactory(
@@ -34600,7 +34605,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const migrationsGetStatusForOrgQuerySchema = z.object({
-    exclude: z.array(z.enum(["repositories"])).optional(),
+    exclude: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.enum(["repositories"])),
+      )
+      .optional(),
   })
 
   const migrationsGetStatusForOrgResponseValidator = responseValidationFactory(
@@ -36241,7 +36251,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
     page: z.coerce.number().optional(),
     sort: z.enum(["created_at"]).optional(),
     direction: z.enum(["asc", "desc"]).optional(),
-    owner: z.array(z.string()).max(10).optional(),
+    owner: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string()).max(10),
+      )
+      .optional(),
     repository: z.string().optional(),
     permission: z.string().optional(),
     last_used_before: z.string().datetime({ offset: true }).optional(),
@@ -36550,7 +36565,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
     page: z.coerce.number().optional(),
     sort: z.enum(["created_at"]).optional(),
     direction: z.enum(["asc", "desc"]).optional(),
-    owner: z.array(z.string()).max(10).optional(),
+    owner: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string()).max(10),
+      )
+      .optional(),
     repository: z.string().optional(),
     permission: z.string().optional(),
     last_used_before: z.string().datetime({ offset: true }).optional(),
@@ -77622,7 +77642,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const migrationsGetStatusForAuthenticatedUserQuerySchema = z.object({
-    exclude: z.array(z.string()).optional(),
+    exclude: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string()),
+      )
+      .optional(),
   })
 
   const migrationsGetStatusForAuthenticatedUserResponseValidator =
diff --git a/integration-tests/typescript-koa/src/generated/azure-core-data-plane-service.tsp/generated.ts b/integration-tests/typescript-koa/src/generated/azure-core-data-plane-service.tsp/generated.ts
index cfe4d3124..4424403db 100644
--- a/integration-tests/typescript-koa/src/generated/azure-core-data-plane-service.tsp/generated.ts
+++ b/integration-tests/typescript-koa/src/generated/azure-core-data-plane-service.tsp/generated.ts
@@ -1040,7 +1040,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
     top: z.coerce.number().optional(),
     skip: z.coerce.number().optional(),
     maxpagesize: z.coerce.number().optional(),
-    select: z.array(z.string()).optional(),
+    select: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string()),
+      )
+      .optional(),
   })
 
   const widgetsListWidgetsResponseValidator = responseValidationFactory(
diff --git a/integration-tests/typescript-koa/src/generated/petstore-expanded.yaml/generated.ts b/integration-tests/typescript-koa/src/generated/petstore-expanded.yaml/generated.ts
index e3e0d0e7d..95c8759ac 100644
--- a/integration-tests/typescript-koa/src/generated/petstore-expanded.yaml/generated.ts
+++ b/integration-tests/typescript-koa/src/generated/petstore-expanded.yaml/generated.ts
@@ -102,7 +102,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const router = new KoaRouter()
 
   const findPetsQuerySchema = z.object({
-    tags: z.array(z.string()).optional(),
+    tags: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string()),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
   })
 
diff --git a/integration-tests/typescript-koa/src/generated/stripe.yaml/generated.ts b/integration-tests/typescript-koa/src/generated/stripe.yaml/generated.ts
index a63895685..c3ebb1a3a 100644
--- a/integration-tests/typescript-koa/src/generated/stripe.yaml/generated.ts
+++ b/integration-tests/typescript-koa/src/generated/stripe.yaml/generated.ts
@@ -13626,7 +13626,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const router = new KoaRouter()
 
   const getAccountQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getAccountBodySchema = z.object({}).optional()
@@ -13908,7 +13913,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().optional(),
   })
@@ -14631,7 +14641,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getAccountsAccountQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getAccountsAccountBodySchema = z.object({}).optional()
@@ -15412,7 +15427,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getAccountsAccountBankAccountsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getAccountsAccountBankAccountsIdBodySchema = z.object({}).optional()
@@ -15557,7 +15577,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getAccountsAccountCapabilitiesQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getAccountsAccountCapabilitiesBodySchema = z.object({}).optional()
@@ -15638,7 +15663,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getAccountsAccountCapabilitiesCapabilityQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getAccountsAccountCapabilitiesCapabilityBodySchema = z
@@ -15769,7 +15799,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getAccountsAccountExternalAccountsQuerySchema = z.object({
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     object: z.enum(["bank_account", "card"]).optional(),
     starting_after: z.string().optional(),
@@ -16006,7 +16041,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getAccountsAccountExternalAccountsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getAccountsAccountExternalAccountsIdBodySchema = z.object({}).optional()
@@ -16211,7 +16251,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getAccountsAccountPeopleQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     relationship: z
       .object({
@@ -16559,7 +16604,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getAccountsAccountPeoplePersonQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getAccountsAccountPeoplePersonBodySchema = z.object({}).optional()
@@ -16820,7 +16870,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getAccountsAccountPersonsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     relationship: z
       .object({
@@ -17168,7 +17223,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getAccountsAccountPersonsPersonQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getAccountsAccountPersonsPersonBodySchema = z.object({}).optional()
@@ -17485,7 +17545,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getApplePayDomainsQuerySchema = z.object({
     domain_name: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -17667,7 +17732,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getApplePayDomainsDomainQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getApplePayDomainsDomainBodySchema = z.object({}).optional()
@@ -17740,7 +17810,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -17818,7 +17893,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getApplicationFeesFeeRefundsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getApplicationFeesFeeRefundsIdBodySchema = z.object({}).optional()
@@ -17938,7 +18018,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getApplicationFeesIdParamSchema = z.object({ id: z.string().max(5000) })
 
   const getApplicationFeesIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getApplicationFeesIdBodySchema = z.object({}).optional()
@@ -18063,7 +18148,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getApplicationFeesIdRefundsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -18202,7 +18292,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getAppsSecretsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     scope: z.object({
       type: z.enum(["account", "user"]),
@@ -18383,7 +18478,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   )
 
   const getAppsSecretsFindQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     name: z.string().max(5000),
     scope: z.object({
       type: z.enum(["account", "user"]),
@@ -18444,7 +18544,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   )
 
   const getBalanceQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getBalanceBodySchema = z.object({}).optional()
@@ -18509,7 +18614,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     currency: z.string().optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     payout: z.string().max(5000).optional(),
     source: z.string().max(5000).optional(),
@@ -18586,7 +18696,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getBalanceHistoryIdParamSchema = z.object({ id: z.string().max(5000) })
 
   const getBalanceHistoryIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getBalanceHistoryIdBodySchema = z.object({}).optional()
@@ -18659,7 +18774,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     currency: z.string().optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     payout: z.string().max(5000).optional(),
     source: z.string().max(5000).optional(),
@@ -18742,7 +18862,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getBalanceTransactionsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getBalanceTransactionsIdBodySchema = z.object({}).optional()
@@ -18911,7 +19036,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getBillingMetersQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z.enum(["active", "inactive"]).optional(),
@@ -19042,7 +19172,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getBillingMetersIdParamSchema = z.object({ id: z.string().max(5000) })
 
   const getBillingMetersIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getBillingMetersIdBodySchema = z.object({}).optional()
@@ -19224,7 +19359,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
     customer: z.string().max(5000),
     end_time: z.coerce.number(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     start_time: z.coerce.number(),
     starting_after: z.string().max(5000).optional(),
@@ -19365,7 +19505,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getBillingPortalConfigurationsQuerySchema = z.object({
     active: PermissiveBoolean.optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     is_default: PermissiveBoolean.optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -19582,7 +19727,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getBillingPortalConfigurationsConfigurationQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getBillingPortalConfigurationsConfigurationBodySchema = z
@@ -19982,7 +20132,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     payment_intent: z.string().max(5000).optional(),
     starting_after: z.string().optional(),
@@ -20169,7 +20324,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getChargesSearchQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     page: z.string().max(5000).optional(),
     query: z.string().max(5000),
@@ -20245,7 +20405,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getChargesChargeParamSchema = z.object({ charge: z.string().max(5000) })
 
   const getChargesChargeQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getChargesChargeBodySchema = z.object({}).optional()
@@ -20455,7 +20620,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getChargesChargeDisputeQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getChargesChargeDisputeBodySchema = z.object({}).optional()
@@ -20736,7 +20906,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getChargesChargeRefundsQuerySchema = z.object({
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().optional(),
   })
@@ -20890,7 +21065,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getChargesChargeRefundsRefundQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getChargesChargeRefundsRefundBodySchema = z.object({}).optional()
@@ -21022,7 +21202,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
     customer: z.string().max(5000).optional(),
     customer_details: z.object({ email: z.string() }).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     payment_intent: z.string().max(5000).optional(),
     payment_link: z.string().max(5000).optional(),
@@ -22116,7 +22301,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCheckoutSessionsSessionQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCheckoutSessionsSessionBodySchema = z.object({}).optional()
@@ -22299,7 +22489,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCheckoutSessionsSessionLineItemsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -22381,7 +22576,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getClimateOrdersQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -22506,7 +22706,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getClimateOrdersOrderQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getClimateOrdersOrderBodySchema = z.object({}).optional()
@@ -22692,7 +22897,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getClimateProductsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -22769,7 +22979,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getClimateProductsProductQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getClimateProductsProductBodySchema = z.object({}).optional()
@@ -22830,7 +23045,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getClimateSuppliersQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -22907,7 +23127,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getClimateSuppliersSupplierQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getClimateSuppliersSupplierBodySchema = z.object({}).optional()
@@ -22969,7 +23194,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getConfirmationTokensConfirmationTokenQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getConfirmationTokensConfirmationTokenBodySchema = z
@@ -23033,7 +23263,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCountrySpecsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -23106,7 +23341,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCountrySpecsCountryQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCountrySpecsCountryBodySchema = z.object({}).optional()
@@ -23178,7 +23418,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -23369,7 +23614,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getCouponsCouponParamSchema = z.object({ coupon: z.string().max(5000) })
 
   const getCouponsCouponQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCouponsCouponBodySchema = z.object({}).optional()
@@ -23499,7 +23749,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     invoice: z.string().max(5000).optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -23668,34 +23923,42 @@ export function createRouter(implementation: Implementation): KoaRouter {
     credit_amount: z.coerce.number().optional(),
     effective_at: z.coerce.number().optional(),
     email_type: z.enum(["credit_note", "none"]).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     invoice: z.string().max(5000),
     lines: z
-      .array(
-        z.object({
-          amount: z.coerce.number().optional(),
-          description: z.string().max(5000).optional(),
-          invoice_line_item: z.string().max(5000).optional(),
-          quantity: z.coerce.number().optional(),
-          tax_amounts: z
-            .union([
-              z.array(
-                z.object({
-                  amount: z.coerce.number(),
-                  tax_rate: z.string().max(5000),
-                  taxable_amount: z.coerce.number(),
-                }),
-              ),
-              z.enum([""]),
-            ])
-            .optional(),
-          tax_rates: z
-            .union([z.array(z.string().max(5000)), z.enum([""])])
-            .optional(),
-          type: z.enum(["custom_line_item", "invoice_line_item"]),
-          unit_amount: z.coerce.number().optional(),
-          unit_amount_decimal: z.string().optional(),
-        }),
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(
+          z.object({
+            amount: z.coerce.number().optional(),
+            description: z.string().max(5000).optional(),
+            invoice_line_item: z.string().max(5000).optional(),
+            quantity: z.coerce.number().optional(),
+            tax_amounts: z
+              .union([
+                z.array(
+                  z.object({
+                    amount: z.coerce.number(),
+                    tax_rate: z.string().max(5000),
+                    taxable_amount: z.coerce.number(),
+                  }),
+                ),
+                z.enum([""]),
+              ])
+              .optional(),
+            tax_rates: z
+              .union([z.array(z.string().max(5000)), z.enum([""])])
+              .optional(),
+            type: z.enum(["custom_line_item", "invoice_line_item"]),
+            unit_amount: z.coerce.number().optional(),
+            unit_amount_decimal: z.string().optional(),
+          }),
+        ),
       )
       .optional(),
     memo: z.string().max(5000).optional(),
@@ -23774,35 +24037,43 @@ export function createRouter(implementation: Implementation): KoaRouter {
     effective_at: z.coerce.number().optional(),
     email_type: z.enum(["credit_note", "none"]).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     invoice: z.string().max(5000),
     limit: z.coerce.number().optional(),
     lines: z
-      .array(
-        z.object({
-          amount: z.coerce.number().optional(),
-          description: z.string().max(5000).optional(),
-          invoice_line_item: z.string().max(5000).optional(),
-          quantity: z.coerce.number().optional(),
-          tax_amounts: z
-            .union([
-              z.array(
-                z.object({
-                  amount: z.coerce.number(),
-                  tax_rate: z.string().max(5000),
-                  taxable_amount: z.coerce.number(),
-                }),
-              ),
-              z.enum([""]),
-            ])
-            .optional(),
-          tax_rates: z
-            .union([z.array(z.string().max(5000)), z.enum([""])])
-            .optional(),
-          type: z.enum(["custom_line_item", "invoice_line_item"]),
-          unit_amount: z.coerce.number().optional(),
-          unit_amount_decimal: z.string().optional(),
-        }),
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(
+          z.object({
+            amount: z.coerce.number().optional(),
+            description: z.string().max(5000).optional(),
+            invoice_line_item: z.string().max(5000).optional(),
+            quantity: z.coerce.number().optional(),
+            tax_amounts: z
+              .union([
+                z.array(
+                  z.object({
+                    amount: z.coerce.number(),
+                    tax_rate: z.string().max(5000),
+                    taxable_amount: z.coerce.number(),
+                  }),
+                ),
+                z.enum([""]),
+              ])
+              .optional(),
+            tax_rates: z
+              .union([z.array(z.string().max(5000)), z.enum([""])])
+              .optional(),
+            type: z.enum(["custom_line_item", "invoice_line_item"]),
+            unit_amount: z.coerce.number().optional(),
+            unit_amount_decimal: z.string().optional(),
+          }),
+        ),
       )
       .optional(),
     memo: z.string().max(5000).optional(),
@@ -23897,7 +24168,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCreditNotesCreditNoteLinesQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -23977,7 +24253,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getCreditNotesIdParamSchema = z.object({ id: z.string().max(5000) })
 
   const getCreditNotesIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCreditNotesIdBodySchema = z.object({}).optional()
@@ -24240,7 +24521,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     email: z.string().max(512).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     test_clock: z.string().max(5000).optional(),
@@ -24529,7 +24815,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersSearchQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     page: z.string().max(5000).optional(),
     query: z.string().max(5000),
@@ -24667,7 +24958,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersCustomerQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCustomersCustomerBodySchema = z.object({}).optional()
@@ -24917,7 +25213,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCustomersCustomerBalanceTransactionsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -25069,7 +25370,14 @@ export function createRouter(implementation: Implementation): KoaRouter {
     z.object({ customer: z.string().max(5000), transaction: z.string() })
 
   const getCustomersCustomerBalanceTransactionsTransactionQuerySchema =
-    z.object({ expand: z.array(z.string().max(5000)).optional() })
+    z.object({
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
+    })
 
   const getCustomersCustomerBalanceTransactionsTransactionBodySchema = z
     .object({})
@@ -25217,7 +25525,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCustomersCustomerBankAccountsQuerySchema = z.object({
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().optional(),
   })
@@ -25468,7 +25781,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersCustomerBankAccountsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCustomersCustomerBankAccountsIdBodySchema = z.object({}).optional()
@@ -25700,7 +26018,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCustomersCustomerCardsQuerySchema = z.object({
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().optional(),
   })
@@ -25946,7 +26269,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersCustomerCardsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCustomersCustomerCardsIdBodySchema = z.object({}).optional()
@@ -26108,7 +26436,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersCustomerCashBalanceQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCustomersCustomerCashBalanceBodySchema = z.object({}).optional()
@@ -26236,7 +26569,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCustomersCustomerCashBalanceTransactionsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -26322,7 +26660,14 @@ export function createRouter(implementation: Implementation): KoaRouter {
     z.object({ customer: z.string().max(5000), transaction: z.string() })
 
   const getCustomersCustomerCashBalanceTransactionsTransactionQuerySchema =
-    z.object({ expand: z.array(z.string().max(5000)).optional() })
+    z.object({
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
+    })
 
   const getCustomersCustomerCashBalanceTransactionsTransactionBodySchema = z
     .object({})
@@ -26452,7 +26797,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersCustomerDiscountQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCustomersCustomerDiscountBodySchema = z.object({}).optional()
@@ -26590,7 +26940,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getCustomersCustomerPaymentMethodsQuerySchema = z.object({
     allow_redisplay: z.enum(["always", "limited", "unspecified"]).optional(),
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().optional(),
     type: z
@@ -26717,7 +27072,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersCustomerPaymentMethodsPaymentMethodQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCustomersCustomerPaymentMethodsPaymentMethodBodySchema = z
@@ -26786,7 +27146,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCustomersCustomerSourcesQuerySchema = z.object({
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     object: z.string().max(5000).optional(),
     starting_after: z.string().optional(),
@@ -27038,7 +27403,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersCustomerSourcesIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCustomersCustomerSourcesIdBodySchema = z.object({}).optional()
@@ -27264,7 +27634,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCustomersCustomerSubscriptionsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -27823,7 +28198,14 @@ export function createRouter(implementation: Implementation): KoaRouter {
     })
 
   const getCustomersCustomerSubscriptionsSubscriptionExposedIdQuerySchema =
-    z.object({ expand: z.array(z.string().max(5000)).optional() })
+    z.object({
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
+    })
 
   const getCustomersCustomerSubscriptionsSubscriptionExposedIdBodySchema = z
     .object({})
@@ -28401,7 +28783,14 @@ export function createRouter(implementation: Implementation): KoaRouter {
     })
 
   const getCustomersCustomerSubscriptionsSubscriptionExposedIdDiscountQuerySchema =
-    z.object({ expand: z.array(z.string().max(5000)).optional() })
+    z.object({
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
+    })
 
   const getCustomersCustomerSubscriptionsSubscriptionExposedIdDiscountBodySchema =
     z.object({}).optional()
@@ -28472,7 +28861,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getCustomersCustomerTaxIdsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -28741,7 +29135,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getCustomersCustomerTaxIdsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getCustomersCustomerTaxIdsIdBodySchema = z.object({}).optional()
@@ -28812,7 +29211,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     payment_intent: z.string().max(5000).optional(),
     starting_after: z.string().max(5000).optional(),
@@ -28886,7 +29290,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getDisputesDisputeQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getDisputesDisputeBodySchema = z.object({}).optional()
@@ -29099,7 +29508,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getEntitlementsActiveEntitlementsQuerySchema = z.object({
     customer: z.string().max(5000),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -29180,7 +29594,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getEntitlementsActiveEntitlementsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getEntitlementsActiveEntitlementsIdBodySchema = z.object({}).optional()
@@ -29246,7 +29665,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getEntitlementsFeaturesQuerySchema = z.object({
     archived: PermissiveBoolean.optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     lookup_key: z.string().max(5000).optional(),
     starting_after: z.string().max(5000).optional(),
@@ -29380,7 +29804,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getEntitlementsFeaturesIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getEntitlementsFeaturesIdBodySchema = z.object({}).optional()
@@ -29626,11 +30055,21 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     delivery_success: PermissiveBoolean.optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     type: z.string().max(5000).optional(),
-    types: z.array(z.string().max(5000)).optional(),
+    types: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getEventsBodySchema = z.object({}).optional()
@@ -29699,7 +30138,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getEventsIdParamSchema = z.object({ id: z.string().max(5000) })
 
   const getEventsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getEventsIdBodySchema = z.object({}).optional()
@@ -29756,7 +30200,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getExchangeRatesQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -29829,7 +30278,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getExchangeRatesRateIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getExchangeRatesRateIdBodySchema = z.object({}).optional()
@@ -29901,7 +30355,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     expired: PermissiveBoolean.optional(),
     file: z.string().max(5000).optional(),
     limit: z.coerce.number().optional(),
@@ -30023,7 +30482,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getFileLinksLinkParamSchema = z.object({ link: z.string() })
 
   const getFileLinksLinkQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getFileLinksLinkBodySchema = z.object({}).optional()
@@ -30153,7 +30617,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     purpose: z
       .enum([
@@ -30309,7 +30778,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getFilesFileParamSchema = z.object({ file: z.string().max(5000) })
 
   const getFilesFileQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getFilesFileBodySchema = z.object({}).optional()
@@ -30372,7 +30846,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       })
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     session: z.string().max(5000).optional(),
     starting_after: z.string().max(5000).optional(),
@@ -30454,7 +30933,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getFinancialConnectionsAccountsAccountQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getFinancialConnectionsAccountsAccountBodySchema = z
@@ -30592,7 +31076,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getFinancialConnectionsAccountsAccountOwnersQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     ownership: z.string().max(5000),
     starting_after: z.string().max(5000).optional(),
@@ -30956,7 +31445,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getFinancialConnectionsSessionsSessionQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getFinancialConnectionsSessionsSessionBodySchema = z
@@ -31024,7 +31518,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getFinancialConnectionsTransactionsQuerySchema = z.object({
     account: z.string().max(5000),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     transacted_at: z
@@ -31120,7 +31619,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getFinancialConnectionsTransactionsTransactionQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getFinancialConnectionsTransactionsTransactionBodySchema = z
@@ -31198,7 +31702,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       })
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -31343,7 +31852,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getForwardingRequestsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getForwardingRequestsIdBodySchema = z.object({}).optional()
@@ -31416,7 +31930,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     type: z.enum(["document", "id_number"]).optional(),
@@ -31499,7 +32018,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIdentityVerificationReportsReportQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIdentityVerificationReportsReportBodySchema = z.object({}).optional()
@@ -31576,7 +32100,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z
@@ -31738,7 +32267,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIdentityVerificationSessionsSessionQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIdentityVerificationSessionsSessionBodySchema = z
@@ -32027,7 +32561,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     invoice: z.string().max(5000).optional(),
     limit: z.coerce.number().optional(),
     pending: PermissiveBoolean.optional(),
@@ -32243,7 +32782,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getInvoiceitemsInvoiceitemQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getInvoiceitemsInvoiceitemBodySchema = z.object({}).optional()
@@ -32429,7 +32973,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z
@@ -33359,7 +33908,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   )
 
   const getInvoicesSearchQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     page: z.string().max(5000).optional(),
     query: z.string().max(5000),
@@ -33581,54 +34135,62 @@ export function createRouter(implementation: Implementation): KoaRouter {
         z.enum([""]),
       ])
       .optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     invoice_items: z
-      .array(
-        z.object({
-          amount: z.coerce.number().optional(),
-          currency: z.string().optional(),
-          description: z.string().max(5000).optional(),
-          discountable: PermissiveBoolean.optional(),
-          discounts: z
-            .union([
-              z.array(
-                z.object({
-                  coupon: z.string().max(5000).optional(),
-                  discount: z.string().max(5000).optional(),
-                  promotion_code: z.string().max(5000).optional(),
-                }),
-              ),
-              z.enum([""]),
-            ])
-            .optional(),
-          invoiceitem: z.string().max(5000).optional(),
-          metadata: z.union([z.record(z.string()), z.enum([""])]).optional(),
-          period: z
-            .object({ end: z.coerce.number(), start: z.coerce.number() })
-            .optional(),
-          price: z.string().max(5000).optional(),
-          price_data: z
-            .object({
-              currency: z.string(),
-              product: z.string().max(5000),
-              tax_behavior: z
-                .enum(["exclusive", "inclusive", "unspecified"])
-                .optional(),
-              unit_amount: z.coerce.number().optional(),
-              unit_amount_decimal: z.string().optional(),
-            })
-            .optional(),
-          quantity: z.coerce.number().optional(),
-          tax_behavior: z
-            .enum(["exclusive", "inclusive", "unspecified"])
-            .optional(),
-          tax_code: z.union([z.string(), z.enum([""])]).optional(),
-          tax_rates: z
-            .union([z.array(z.string().max(5000)), z.enum([""])])
-            .optional(),
-          unit_amount: z.coerce.number().optional(),
-          unit_amount_decimal: z.string().optional(),
-        }),
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(
+          z.object({
+            amount: z.coerce.number().optional(),
+            currency: z.string().optional(),
+            description: z.string().max(5000).optional(),
+            discountable: PermissiveBoolean.optional(),
+            discounts: z
+              .union([
+                z.array(
+                  z.object({
+                    coupon: z.string().max(5000).optional(),
+                    discount: z.string().max(5000).optional(),
+                    promotion_code: z.string().max(5000).optional(),
+                  }),
+                ),
+                z.enum([""]),
+              ])
+              .optional(),
+            invoiceitem: z.string().max(5000).optional(),
+            metadata: z.union([z.record(z.string()), z.enum([""])]).optional(),
+            period: z
+              .object({ end: z.coerce.number(), start: z.coerce.number() })
+              .optional(),
+            price: z.string().max(5000).optional(),
+            price_data: z
+              .object({
+                currency: z.string(),
+                product: z.string().max(5000),
+                tax_behavior: z
+                  .enum(["exclusive", "inclusive", "unspecified"])
+                  .optional(),
+                unit_amount: z.coerce.number().optional(),
+                unit_amount_decimal: z.string().optional(),
+              })
+              .optional(),
+            quantity: z.coerce.number().optional(),
+            tax_behavior: z
+              .enum(["exclusive", "inclusive", "unspecified"])
+              .optional(),
+            tax_code: z.union([z.string(), z.enum([""])]).optional(),
+            tax_rates: z
+              .union([z.array(z.string().max(5000)), z.enum([""])])
+              .optional(),
+            unit_amount: z.coerce.number().optional(),
+            unit_amount_decimal: z.string().optional(),
+          }),
+        ),
       )
       .optional(),
     issuer: z
@@ -33894,48 +34456,51 @@ export function createRouter(implementation: Implementation): KoaRouter {
       })
       .optional(),
     subscription_items: z
-      .array(
-        z.object({
-          billing_thresholds: z
-            .union([z.object({ usage_gte: z.coerce.number() }), z.enum([""])])
-            .optional(),
-          clear_usage: PermissiveBoolean.optional(),
-          deleted: PermissiveBoolean.optional(),
-          discounts: z
-            .union([
-              z.array(
-                z.object({
-                  coupon: z.string().max(5000).optional(),
-                  discount: z.string().max(5000).optional(),
-                  promotion_code: z.string().max(5000).optional(),
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(
+          z.object({
+            billing_thresholds: z
+              .union([z.object({ usage_gte: z.coerce.number() }), z.enum([""])])
+              .optional(),
+            clear_usage: PermissiveBoolean.optional(),
+            deleted: PermissiveBoolean.optional(),
+            discounts: z
+              .union([
+                z.array(
+                  z.object({
+                    coupon: z.string().max(5000).optional(),
+                    discount: z.string().max(5000).optional(),
+                    promotion_code: z.string().max(5000).optional(),
+                  }),
+                ),
+                z.enum([""]),
+              ])
+              .optional(),
+            id: z.string().max(5000).optional(),
+            metadata: z.union([z.record(z.string()), z.enum([""])]).optional(),
+            price: z.string().max(5000).optional(),
+            price_data: z
+              .object({
+                currency: z.string(),
+                product: z.string().max(5000),
+                recurring: z.object({
+                  interval: z.enum(["day", "month", "week", "year"]),
+                  interval_count: z.coerce.number().optional(),
                 }),
-              ),
-              z.enum([""]),
-            ])
-            .optional(),
-          id: z.string().max(5000).optional(),
-          metadata: z.union([z.record(z.string()), z.enum([""])]).optional(),
-          price: z.string().max(5000).optional(),
-          price_data: z
-            .object({
-              currency: z.string(),
-              product: z.string().max(5000),
-              recurring: z.object({
-                interval: z.enum(["day", "month", "week", "year"]),
-                interval_count: z.coerce.number().optional(),
-              }),
-              tax_behavior: z
-                .enum(["exclusive", "inclusive", "unspecified"])
-                .optional(),
-              unit_amount: z.coerce.number().optional(),
-              unit_amount_decimal: z.string().optional(),
-            })
-            .optional(),
-          quantity: z.coerce.number().optional(),
-          tax_rates: z
-            .union([z.array(z.string().max(5000)), z.enum([""])])
-            .optional(),
-        }),
+                tax_behavior: z
+                  .enum(["exclusive", "inclusive", "unspecified"])
+                  .optional(),
+                unit_amount: z.coerce.number().optional(),
+                unit_amount_decimal: z.string().optional(),
+              })
+              .optional(),
+            quantity: z.coerce.number().optional(),
+            tax_rates: z
+              .union([z.array(z.string().max(5000)), z.enum([""])])
+              .optional(),
+          }),
+        ),
       )
       .optional(),
     subscription_proration_behavior: z
@@ -34151,54 +34716,62 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     invoice_items: z
-      .array(
-        z.object({
-          amount: z.coerce.number().optional(),
-          currency: z.string().optional(),
-          description: z.string().max(5000).optional(),
-          discountable: PermissiveBoolean.optional(),
-          discounts: z
-            .union([
-              z.array(
-                z.object({
-                  coupon: z.string().max(5000).optional(),
-                  discount: z.string().max(5000).optional(),
-                  promotion_code: z.string().max(5000).optional(),
-                }),
-              ),
-              z.enum([""]),
-            ])
-            .optional(),
-          invoiceitem: z.string().max(5000).optional(),
-          metadata: z.union([z.record(z.string()), z.enum([""])]).optional(),
-          period: z
-            .object({ end: z.coerce.number(), start: z.coerce.number() })
-            .optional(),
-          price: z.string().max(5000).optional(),
-          price_data: z
-            .object({
-              currency: z.string(),
-              product: z.string().max(5000),
-              tax_behavior: z
-                .enum(["exclusive", "inclusive", "unspecified"])
-                .optional(),
-              unit_amount: z.coerce.number().optional(),
-              unit_amount_decimal: z.string().optional(),
-            })
-            .optional(),
-          quantity: z.coerce.number().optional(),
-          tax_behavior: z
-            .enum(["exclusive", "inclusive", "unspecified"])
-            .optional(),
-          tax_code: z.union([z.string(), z.enum([""])]).optional(),
-          tax_rates: z
-            .union([z.array(z.string().max(5000)), z.enum([""])])
-            .optional(),
-          unit_amount: z.coerce.number().optional(),
-          unit_amount_decimal: z.string().optional(),
-        }),
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(
+          z.object({
+            amount: z.coerce.number().optional(),
+            currency: z.string().optional(),
+            description: z.string().max(5000).optional(),
+            discountable: PermissiveBoolean.optional(),
+            discounts: z
+              .union([
+                z.array(
+                  z.object({
+                    coupon: z.string().max(5000).optional(),
+                    discount: z.string().max(5000).optional(),
+                    promotion_code: z.string().max(5000).optional(),
+                  }),
+                ),
+                z.enum([""]),
+              ])
+              .optional(),
+            invoiceitem: z.string().max(5000).optional(),
+            metadata: z.union([z.record(z.string()), z.enum([""])]).optional(),
+            period: z
+              .object({ end: z.coerce.number(), start: z.coerce.number() })
+              .optional(),
+            price: z.string().max(5000).optional(),
+            price_data: z
+              .object({
+                currency: z.string(),
+                product: z.string().max(5000),
+                tax_behavior: z
+                  .enum(["exclusive", "inclusive", "unspecified"])
+                  .optional(),
+                unit_amount: z.coerce.number().optional(),
+                unit_amount_decimal: z.string().optional(),
+              })
+              .optional(),
+            quantity: z.coerce.number().optional(),
+            tax_behavior: z
+              .enum(["exclusive", "inclusive", "unspecified"])
+              .optional(),
+            tax_code: z.union([z.string(), z.enum([""])]).optional(),
+            tax_rates: z
+              .union([z.array(z.string().max(5000)), z.enum([""])])
+              .optional(),
+            unit_amount: z.coerce.number().optional(),
+            unit_amount_decimal: z.string().optional(),
+          }),
+        ),
       )
       .optional(),
     issuer: z
@@ -34466,48 +35039,51 @@ export function createRouter(implementation: Implementation): KoaRouter {
       })
       .optional(),
     subscription_items: z
-      .array(
-        z.object({
-          billing_thresholds: z
-            .union([z.object({ usage_gte: z.coerce.number() }), z.enum([""])])
-            .optional(),
-          clear_usage: PermissiveBoolean.optional(),
-          deleted: PermissiveBoolean.optional(),
-          discounts: z
-            .union([
-              z.array(
-                z.object({
-                  coupon: z.string().max(5000).optional(),
-                  discount: z.string().max(5000).optional(),
-                  promotion_code: z.string().max(5000).optional(),
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(
+          z.object({
+            billing_thresholds: z
+              .union([z.object({ usage_gte: z.coerce.number() }), z.enum([""])])
+              .optional(),
+            clear_usage: PermissiveBoolean.optional(),
+            deleted: PermissiveBoolean.optional(),
+            discounts: z
+              .union([
+                z.array(
+                  z.object({
+                    coupon: z.string().max(5000).optional(),
+                    discount: z.string().max(5000).optional(),
+                    promotion_code: z.string().max(5000).optional(),
+                  }),
+                ),
+                z.enum([""]),
+              ])
+              .optional(),
+            id: z.string().max(5000).optional(),
+            metadata: z.union([z.record(z.string()), z.enum([""])]).optional(),
+            price: z.string().max(5000).optional(),
+            price_data: z
+              .object({
+                currency: z.string(),
+                product: z.string().max(5000),
+                recurring: z.object({
+                  interval: z.enum(["day", "month", "week", "year"]),
+                  interval_count: z.coerce.number().optional(),
                 }),
-              ),
-              z.enum([""]),
-            ])
-            .optional(),
-          id: z.string().max(5000).optional(),
-          metadata: z.union([z.record(z.string()), z.enum([""])]).optional(),
-          price: z.string().max(5000).optional(),
-          price_data: z
-            .object({
-              currency: z.string(),
-              product: z.string().max(5000),
-              recurring: z.object({
-                interval: z.enum(["day", "month", "week", "year"]),
-                interval_count: z.coerce.number().optional(),
-              }),
-              tax_behavior: z
-                .enum(["exclusive", "inclusive", "unspecified"])
-                .optional(),
-              unit_amount: z.coerce.number().optional(),
-              unit_amount_decimal: z.string().optional(),
-            })
-            .optional(),
-          quantity: z.coerce.number().optional(),
-          tax_rates: z
-            .union([z.array(z.string().max(5000)), z.enum([""])])
-            .optional(),
-        }),
+                tax_behavior: z
+                  .enum(["exclusive", "inclusive", "unspecified"])
+                  .optional(),
+                unit_amount: z.coerce.number().optional(),
+                unit_amount_decimal: z.string().optional(),
+              })
+              .optional(),
+            quantity: z.coerce.number().optional(),
+            tax_rates: z
+              .union([z.array(z.string().max(5000)), z.enum([""])])
+              .optional(),
+          }),
+        ),
       )
       .optional(),
     subscription_proration_behavior: z
@@ -34649,7 +35225,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getInvoicesInvoiceQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getInvoicesInvoiceBodySchema = z.object({}).optional()
@@ -35288,7 +35869,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getInvoicesInvoiceLinesQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -35967,7 +36553,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z.enum(["closed", "pending", "reversed"]).optional(),
@@ -36048,7 +36639,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIssuingAuthorizationsAuthorizationQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIssuingAuthorizationsAuthorizationBodySchema = z
@@ -36311,7 +36907,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     email: z.string().optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     phone_number: z.string().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -37425,7 +38026,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIssuingCardholdersCardholderQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIssuingCardholdersCardholderBodySchema = z.object({}).optional()
@@ -38537,7 +39143,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
     ending_before: z.string().max(5000).optional(),
     exp_month: z.coerce.number().optional(),
     exp_year: z.coerce.number().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     last4: z.string().max(5000).optional(),
     limit: z.coerce.number().optional(),
     personalization_design: z.string().max(5000).optional(),
@@ -39628,7 +40239,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIssuingCardsCardQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIssuingCardsCardBodySchema = z.object({}).optional()
@@ -40720,7 +41336,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z
@@ -41035,7 +41656,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIssuingDisputesDisputeQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIssuingDisputesDisputeBodySchema = z.object({}).optional()
@@ -41395,9 +42021,19 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getIssuingPersonalizationDesignsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
-    lookup_keys: z.array(z.string().max(200)).optional(),
+    lookup_keys: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(200)),
+      )
+      .optional(),
     preferences: z
       .object({
         is_default: PermissiveBoolean.optional(),
@@ -41552,7 +42188,14 @@ export function createRouter(implementation: Implementation): KoaRouter {
     z.object({ personalization_design: z.string().max(5000) })
 
   const getIssuingPersonalizationDesignsPersonalizationDesignQuerySchema =
-    z.object({ expand: z.array(z.string().max(5000)).optional() })
+    z.object({
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
+    })
 
   const getIssuingPersonalizationDesignsPersonalizationDesignBodySchema = z
     .object({})
@@ -41717,7 +42360,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getIssuingPhysicalBundlesQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z.enum(["active", "inactive", "review"]).optional(),
@@ -41799,7 +42447,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIssuingPhysicalBundlesPhysicalBundleQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIssuingPhysicalBundlesPhysicalBundleBodySchema = z
@@ -41866,7 +42519,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIssuingSettlementsSettlementQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIssuingSettlementsSettlementBodySchema = z.object({}).optional()
@@ -41996,7 +42654,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z.enum(["active", "deleted", "requested", "suspended"]).optional(),
@@ -42070,7 +42733,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIssuingTokensTokenQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIssuingTokensTokenBodySchema = z.object({}).optional()
@@ -42203,7 +42871,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     type: z.enum(["capture", "refund"]).optional(),
@@ -42284,7 +42957,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getIssuingTransactionsTransactionQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getIssuingTransactionsTransactionBodySchema = z.object({}).optional()
@@ -42489,7 +43167,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getLinkAccountSessionsSessionQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getLinkAccountSessionsSessionBodySchema = z.object({}).optional()
@@ -42557,7 +43240,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       })
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     session: z.string().max(5000).optional(),
     starting_after: z.string().max(5000).optional(),
@@ -42634,7 +43322,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getLinkedAccountsAccountQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getLinkedAccountsAccountBodySchema = z.object({}).optional()
@@ -42761,7 +43454,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getLinkedAccountsAccountOwnersQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     ownership: z.string().max(5000),
     starting_after: z.string().max(5000).optional(),
@@ -42902,7 +43600,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getMandatesMandateParamSchema = z.object({ mandate: z.string() })
 
   const getMandatesMandateQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getMandatesMandateBodySchema = z.object({}).optional()
@@ -42975,7 +43678,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -44055,7 +44763,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   )
 
   const getPaymentIntentsSearchQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     page: z.string().max(5000).optional(),
     query: z.string().max(5000),
@@ -44138,7 +44851,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getPaymentIntentsIntentQuerySchema = z.object({
     client_secret: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPaymentIntentsIntentBodySchema = z.object({}).optional()
@@ -46541,7 +47259,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getPaymentLinksQuerySchema = z.object({
     active: PermissiveBoolean.optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -47144,7 +47867,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getPaymentLinksPaymentLinkQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPaymentLinksPaymentLinkBodySchema = z.object({}).optional()
@@ -47750,7 +48478,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getPaymentLinksPaymentLinkLineItemsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -47833,7 +48566,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getPaymentMethodConfigurationsQuerySchema = z.object({
     application: z.union([z.string().max(100), z.enum([""])]).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -48256,7 +48994,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getPaymentMethodConfigurationsConfigurationQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPaymentMethodConfigurationsConfigurationBodySchema = z
@@ -48678,7 +49421,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
     domain_name: z.string().max(5000).optional(),
     enabled: PermissiveBoolean.optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -48810,7 +49558,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getPaymentMethodDomainsPaymentMethodDomainQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPaymentMethodDomainsPaymentMethodDomainBodySchema = z
@@ -49000,7 +49753,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getPaymentMethodsQuerySchema = z.object({
     customer: z.string().max(5000).optional(),
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().optional(),
     type: z
@@ -49443,7 +50201,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getPaymentMethodsPaymentMethodQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPaymentMethodsPaymentMethodBodySchema = z.object({}).optional()
@@ -49744,7 +50507,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     destination: z.string().optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z.string().max(5000).optional(),
@@ -49870,7 +50638,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getPayoutsPayoutParamSchema = z.object({ payout: z.string().max(5000) })
 
   const getPayoutsPayoutQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPayoutsPayoutBodySchema = z.object({}).optional()
@@ -50115,7 +50888,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     product: z.string().max(5000).optional(),
     starting_after: z.string().max(5000).optional(),
@@ -50328,7 +51106,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getPlansPlanParamSchema = z.object({ plan: z.string().max(5000) })
 
   const getPlansPlanQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPlansPlanBodySchema = z.object({}).optional()
@@ -50457,9 +51240,19 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     currency: z.string().optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
-    lookup_keys: z.array(z.string().max(5000)).optional(),
+    lookup_keys: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     product: z.string().max(5000).optional(),
     recurring: z
       .object({
@@ -50668,7 +51461,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getPricesSearchQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     page: z.string().max(5000).optional(),
     query: z.string().max(5000),
@@ -50744,7 +51542,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getPricesPriceParamSchema = z.object({ price: z.string().max(5000) })
 
   const getPricesPriceQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPricesPriceBodySchema = z.object({}).optional()
@@ -50908,8 +51711,18 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
-    ids: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
+    ids: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     shippable: PermissiveBoolean.optional(),
     starting_after: z.string().max(5000).optional(),
@@ -51094,7 +51907,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getProductsSearchQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     page: z.string().max(5000).optional(),
     query: z.string().max(5000),
@@ -51220,7 +52038,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getProductsIdParamSchema = z.object({ id: z.string().max(5000) })
 
   const getProductsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getProductsIdBodySchema = z.object({}).optional()
@@ -51363,7 +52186,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getProductsProductFeaturesQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -51557,7 +52385,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getProductsProductFeaturesIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getProductsProductFeaturesIdBodySchema = z.object({}).optional()
@@ -51631,7 +52464,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -51771,7 +52609,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getPromotionCodesPromotionCodeQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getPromotionCodesPromotionCodeBodySchema = z.object({}).optional()
@@ -51898,7 +52741,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getQuotesQuerySchema = z.object({
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z.enum(["accepted", "canceled", "draft", "open"]).optional(),
@@ -52145,7 +52993,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getQuotesQuoteParamSchema = z.object({ quote: z.string().max(5000) })
 
   const getQuotesQuoteQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getQuotesQuoteBodySchema = z.object({}).optional()
@@ -52496,7 +53349,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getQuotesQuoteComputedUpfrontLineItemsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -52645,7 +53503,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getQuotesQuoteLineItemsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -52724,7 +53587,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getQuotesQuotePdfParamSchema = z.object({ quote: z.string().max(5000) })
 
   const getQuotesQuotePdfQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getQuotesQuotePdfBodySchema = z.object({}).optional()
@@ -52797,7 +53665,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     payment_intent: z.string().max(5000).optional(),
     starting_after: z.string().max(5000).optional(),
@@ -52878,7 +53751,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getRadarEarlyFraudWarningsEarlyFraudWarningQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getRadarEarlyFraudWarningsEarlyFraudWarningBodySchema = z
@@ -52953,7 +53831,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     value: z.string().max(800).optional(),
@@ -53144,7 +54027,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getRadarValueListItemsItemQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getRadarValueListItemsItemBodySchema = z.object({}).optional()
@@ -53218,7 +54106,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -53416,7 +54309,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getRadarValueListsValueListQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getRadarValueListsValueListBodySchema = z.object({}).optional()
@@ -53548,7 +54446,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     payment_intent: z.string().max(5000).optional(),
     starting_after: z.string().optional(),
@@ -53681,7 +54584,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getRefundsRefundParamSchema = z.object({ refund: z.string() })
 
   const getRefundsRefundQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getRefundsRefundBodySchema = z.object({}).optional()
@@ -53860,7 +54768,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -54644,7 +55557,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getReportingReportRunsReportRunQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getReportingReportRunsReportRunBodySchema = z.object({}).optional()
@@ -54702,7 +55620,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   )
 
   const getReportingReportTypesQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getReportingReportTypesBodySchema = z.object({}).optional()
@@ -54777,7 +55700,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getReportingReportTypesReportTypeQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getReportingReportTypesReportTypeBodySchema = z.object({}).optional()
@@ -54850,7 +55778,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -54921,7 +55854,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getReviewsReviewParamSchema = z.object({ review: z.string().max(5000) })
 
   const getReviewsReviewQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getReviewsReviewBodySchema = z.object({}).optional()
@@ -55047,7 +55985,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     setup_intent: z.string().max(5000),
     starting_after: z.string().max(5000).optional(),
@@ -55131,7 +56074,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     payment_method: z.string().max(5000).optional(),
     starting_after: z.string().max(5000).optional(),
@@ -55700,7 +56648,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getSetupIntentsIntentQuerySchema = z.object({
     client_secret: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getSetupIntentsIntentBodySchema = z.object({}).optional()
@@ -56867,7 +57820,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     currency: z.string().optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -57023,7 +57981,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getShippingRatesShippingRateTokenQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getShippingRatesShippingRateTokenBodySchema = z.object({}).optional()
@@ -57165,7 +58128,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getSigmaScheduledQueryRunsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -57245,7 +58213,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getSigmaScheduledQueryRunsScheduledQueryRunQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getSigmaScheduledQueryRunsScheduledQueryRunBodySchema = z
@@ -57461,7 +58434,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getSourcesSourceQuerySchema = z.object({
     client_secret: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getSourcesSourceBodySchema = z.object({}).optional()
@@ -57663,7 +58641,14 @@ export function createRouter(implementation: Implementation): KoaRouter {
     })
 
   const getSourcesSourceMandateNotificationsMandateNotificationQuerySchema =
-    z.object({ expand: z.array(z.string().max(5000)).optional() })
+    z.object({
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
+    })
 
   const getSourcesSourceMandateNotificationsMandateNotificationBodySchema = z
     .object({})
@@ -57735,7 +58720,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getSourcesSourceSourceTransactionsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -57822,7 +58812,14 @@ export function createRouter(implementation: Implementation): KoaRouter {
     })
 
   const getSourcesSourceSourceTransactionsSourceTransactionQuerySchema =
-    z.object({ expand: z.array(z.string().max(5000)).optional() })
+    z.object({
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
+    })
 
   const getSourcesSourceSourceTransactionsSourceTransactionBodySchema = z
     .object({})
@@ -57949,7 +58946,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getSubscriptionItemsQuerySchema = z.object({
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().optional(),
     subscription: z.string().max(5000),
@@ -58191,7 +59193,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getSubscriptionItemsItemQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getSubscriptionItemsItemBodySchema = z.object({}).optional()
@@ -58365,7 +59372,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getSubscriptionItemsSubscriptionItemUsageRecordSummariesQuerySchema =
     z.object({
       ending_before: z.string().max(5000).optional(),
-      expand: z.array(z.string().max(5000)).optional(),
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
       limit: z.coerce.number().optional(),
       starting_after: z.string().max(5000).optional(),
     })
@@ -58555,7 +59567,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     released_at: z
       .union([
@@ -58916,7 +59933,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getSubscriptionSchedulesScheduleQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getSubscriptionSchedulesScheduleBodySchema = z.object({}).optional()
@@ -59418,7 +60440,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     price: z.string().max(5000).optional(),
     starting_after: z.string().max(5000).optional(),
@@ -59898,7 +60925,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getSubscriptionsSearchQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     page: z.string().max(5000).optional(),
     query: z.string().max(5000),
@@ -60061,7 +61093,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getSubscriptionsSubscriptionExposedIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getSubscriptionsSubscriptionExposedIdBodySchema = z
@@ -60876,7 +61913,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTaxCalculationsCalculationLineItemsQuerySchema = z.object({
     ending_before: z.string().max(500).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(500).optional(),
   })
@@ -60963,7 +62005,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTaxRegistrationsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z.enum(["active", "all", "expired", "scheduled"]).optional(),
@@ -61418,7 +62465,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTaxRegistrationsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTaxRegistrationsIdBodySchema = z.object({}).optional()
@@ -61542,7 +62594,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   )
 
   const getTaxSettingsQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTaxSettingsBodySchema = z.object({}).optional()
@@ -61792,7 +62849,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTaxTransactionsTransactionQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTaxTransactionsTransactionBodySchema = z.object({}).optional()
@@ -61855,7 +62917,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTaxTransactionsTransactionLineItemsQuerySchema = z.object({
     ending_before: z.string().max(500).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(500).optional(),
   })
@@ -61942,7 +63009,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTaxCodesQuerySchema = z.object({
     ending_before: z.string().optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().optional(),
   })
@@ -62013,7 +63085,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getTaxCodesIdParamSchema = z.object({ id: z.string().max(5000) })
 
   const getTaxCodesIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTaxCodesIdBodySchema = z.object({}).optional()
@@ -62070,7 +63147,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTaxIdsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     owner: z
       .object({
@@ -62327,7 +63409,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getTaxIdsIdParamSchema = z.object({ id: z.string().max(5000) })
 
   const getTaxIdsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTaxIdsIdBodySchema = z.object({}).optional()
@@ -62396,7 +63483,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     inclusive: PermissiveBoolean.optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -62541,7 +63633,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTaxRatesTaxRateQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTaxRatesTaxRateBodySchema = z.object({}).optional()
@@ -62685,7 +63782,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTerminalConfigurationsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     is_account_default: PermissiveBoolean.optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -63007,7 +64109,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTerminalConfigurationsConfigurationQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTerminalConfigurationsConfigurationBodySchema = z
@@ -63351,7 +64458,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTerminalLocationsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -63546,7 +64658,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTerminalLocationsLocationQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTerminalLocationsLocationBodySchema = z.object({}).optional()
@@ -63700,7 +64817,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     location: z.string().max(5000).optional(),
     serial_number: z.string().max(5000).optional(),
@@ -63888,7 +65010,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTerminalReadersReaderQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTerminalReadersReaderBodySchema = z.object({}).optional()
@@ -67355,7 +68482,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTestHelpersTestClocksQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -67547,7 +68679,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTestHelpersTestClocksTestClockQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTestHelpersTestClocksTestClockBodySchema = z.object({}).optional()
@@ -68997,7 +70134,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getTokensTokenParamSchema = z.object({ token: z.string().max(5000) })
 
   const getTokensTokenQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTokensTokenBodySchema = z.object({}).optional()
@@ -69076,7 +70218,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     status: z.enum(["canceled", "failed", "pending", "succeeded"]).optional(),
@@ -69201,7 +70348,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   const getTopupsTopupParamSchema = z.object({ topup: z.string().max(5000) })
 
   const getTopupsTopupQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTopupsTopupBodySchema = z.object({}).optional()
@@ -69384,7 +70536,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     destination: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
     transfer_group: z.string().max(5000).optional(),
@@ -69513,7 +70670,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTransfersIdReversalsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -69658,7 +70820,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTransfersTransferQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTransfersTransferBodySchema = z.object({}).optional()
@@ -69785,7 +70952,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTransfersTransferReversalsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTransfersTransferReversalsIdBodySchema = z.object({}).optional()
@@ -69904,7 +71076,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTreasuryCreditReversalsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     received_credit: z.string().max(5000).optional(),
@@ -70034,7 +71211,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryCreditReversalsCreditReversalQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryCreditReversalsCreditReversalBodySchema = z
@@ -70098,7 +71280,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTreasuryDebitReversalsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     received_debit: z.string().max(5000).optional(),
@@ -70231,7 +71418,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryDebitReversalsDebitReversalQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryDebitReversalsDebitReversalBodySchema = z
@@ -70306,7 +71498,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -70480,7 +71677,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryFinancialAccountsFinancialAccountQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryFinancialAccountsFinancialAccountBodySchema = z
@@ -70651,7 +71853,14 @@ export function createRouter(implementation: Implementation): KoaRouter {
     z.object({ financial_account: z.string().max(5000) })
 
   const getTreasuryFinancialAccountsFinancialAccountFeaturesQuerySchema =
-    z.object({ expand: z.array(z.string().max(5000)).optional() })
+    z.object({
+      expand: z
+        .preprocess(
+          (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+          z.array(z.string().max(5000)),
+        )
+        .optional(),
+    })
 
   const getTreasuryFinancialAccountsFinancialAccountFeaturesBodySchema = z
     .object({})
@@ -70819,7 +72028,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTreasuryInboundTransfersQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -70956,7 +72170,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryInboundTransfersIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryInboundTransfersIdBodySchema = z.object({}).optional()
@@ -71091,7 +72310,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       .optional(),
     customer: z.string().max(5000).optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -71283,7 +72507,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryOutboundPaymentsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryOutboundPaymentsIdBodySchema = z.object({}).optional()
@@ -71401,7 +72630,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTreasuryOutboundTransfersQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -71550,7 +72784,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryOutboundTransfersOutboundTransferQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryOutboundTransfersOutboundTransferBodySchema = z
@@ -71677,7 +72916,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTreasuryReceivedCreditsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     linked_flows: z
@@ -71766,7 +73010,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryReceivedCreditsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryReceivedCreditsIdBodySchema = z.object({}).optional()
@@ -71825,7 +73074,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTreasuryReceivedDebitsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
@@ -71904,7 +73158,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryReceivedDebitsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryReceivedDebitsIdBodySchema = z.object({}).optional()
@@ -71985,7 +73244,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     order_by: z.enum(["created", "effective_at"]).optional(),
@@ -72069,7 +73333,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryTransactionEntriesIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryTransactionEntriesIdBodySchema = z.object({}).optional()
@@ -72139,7 +73408,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
       ])
       .optional(),
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     financial_account: z.string(),
     limit: z.coerce.number().optional(),
     order_by: z.enum(["created", "posted_at"]).optional(),
@@ -72234,7 +73508,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getTreasuryTransactionsIdQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getTreasuryTransactionsIdBodySchema = z.object({}).optional()
@@ -72295,7 +73574,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getWebhookEndpointsQuerySchema = z.object({
     ending_before: z.string().max(5000).optional(),
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
     limit: z.coerce.number().optional(),
     starting_after: z.string().max(5000).optional(),
   })
@@ -72832,7 +74116,12 @@ export function createRouter(implementation: Implementation): KoaRouter {
   })
 
   const getWebhookEndpointsWebhookEndpointQuerySchema = z.object({
-    expand: z.array(z.string().max(5000)).optional(),
+    expand: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string().max(5000)),
+      )
+      .optional(),
   })
 
   const getWebhookEndpointsWebhookEndpointBodySchema = z.object({}).optional()
diff --git a/integration-tests/typescript-koa/src/generated/todo-lists.yaml/generated.ts b/integration-tests/typescript-koa/src/generated/todo-lists.yaml/generated.ts
index 59fda38b4..14694e293 100644
--- a/integration-tests/typescript-koa/src/generated/todo-lists.yaml/generated.ts
+++ b/integration-tests/typescript-koa/src/generated/todo-lists.yaml/generated.ts
@@ -14,7 +14,12 @@ import {
   t_UpdateTodoListByIdBodySchema,
   t_UpdateTodoListByIdParamSchema,
 } from "./models"
-import { s_CreateUpdateTodoList, s_Error, s_TodoList } from "./schemas"
+import {
+  s_CreateUpdateTodoList,
+  s_Error,
+  s_Statuses,
+  s_TodoList,
+} from "./schemas"
 import KoaRouter, { RouterContext } from "@koa/router"
 import {
   KoaRuntimeError,
@@ -167,7 +172,18 @@ export function createRouter(implementation: Implementation): KoaRouter {
 
   const getTodoListsQuerySchema = z.object({
     created: z.string().datetime({ offset: true }).optional(),
-    status: z.enum(["incomplete", "complete"]).optional(),
+    statuses: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        s_Statuses,
+      )
+      .optional(),
+    tags: z
+      .preprocess(
+        (it: unknown) => (Array.isArray(it) || it === undefined ? it : [it]),
+        z.array(z.string()),
+      )
+      .optional(),
   })
 
   const getTodoListsResponseValidator = responseValidationFactory(
diff --git a/integration-tests/typescript-koa/src/generated/todo-lists.yaml/models.ts b/integration-tests/typescript-koa/src/generated/todo-lists.yaml/models.ts
index da6dcb289..1422b3d08 100644
--- a/integration-tests/typescript-koa/src/generated/todo-lists.yaml/models.ts
+++ b/integration-tests/typescript-koa/src/generated/todo-lists.yaml/models.ts
@@ -7,6 +7,8 @@ export type t_Error = {
   message?: string
 }
 
+export type t_Statuses = ("incomplete" | "complete")[]
+
 export type t_TodoList = {
   created: string
   id: string
@@ -40,7 +42,8 @@ export type t_GetTodoListItemsParamSchema = {
 
 export type t_GetTodoListsQuerySchema = {
   created?: string
-  status?: "incomplete" | "complete"
+  statuses?: t_Statuses
+  tags?: string[]
 }
 
 export type t_UpdateTodoListByIdBodySchema = {
diff --git a/integration-tests/typescript-koa/src/generated/todo-lists.yaml/schemas.ts b/integration-tests/typescript-koa/src/generated/todo-lists.yaml/schemas.ts
index 3c99ec6ce..d1fecbd05 100644
--- a/integration-tests/typescript-koa/src/generated/todo-lists.yaml/schemas.ts
+++ b/integration-tests/typescript-koa/src/generated/todo-lists.yaml/schemas.ts
@@ -6,6 +6,8 @@ import { z } from "zod"
 
 export const s_CreateUpdateTodoList = z.object({ name: z.string() })
 
+export const s_Statuses = z.array(z.enum(["incomplete", "complete"]))
+
 export const s_TodoList = z.object({
   id: z.string(),
   name: z.string(),
diff --git a/integration-tests/typescript-koa/src/petstore-expanded.yaml.ts b/integration-tests/typescript-koa/src/petstore-expanded.yaml.ts
index 934c30025..0aa96cb75 100644
--- a/integration-tests/typescript-koa/src/petstore-expanded.yaml.ts
+++ b/integration-tests/typescript-koa/src/petstore-expanded.yaml.ts
@@ -10,7 +10,7 @@ import {ZodError} from "zod"
 import {KoaRuntimeResponder} from "@nahkies/typescript-koa-runtime/server"
 import {t_Error} from "./generated/petstore-expanded.yaml/models"
 
-const notImplemented = async (
+export const notImplemented = async (
   _: unknown,
   respond: KoaRuntimeResponder<501, t_Error>,
 ) => {
diff --git a/integration-tests/typescript-koa/src/todo-lists.yaml.ts b/integration-tests/typescript-koa/src/todo-lists.yaml.ts
new file mode 100644
index 000000000..4103c7d8a
--- /dev/null
+++ b/integration-tests/typescript-koa/src/todo-lists.yaml.ts
@@ -0,0 +1,41 @@
+import {
+  bootstrap,
+  createRouter,
+  GetTodoLists,
+} from "./generated/todo-lists.yaml/generated"
+import {genericErrorMiddleware, notImplemented} from "./petstore-expanded.yaml"
+import {t_TodoList} from "./generated/todo-lists.yaml/models"
+
+const getTodoLists: GetTodoLists = async ({query}, respond)=>{
+  console.info('query', {query})
+  return respond.with200().body([] as t_TodoList[])
+}
+
+async function main() {
+  const {server, address} = await bootstrap({
+    router: createRouter({
+      getTodoLists,
+      getTodoListById: notImplemented,
+      updateTodoListById: notImplemented,
+      deleteTodoListById: notImplemented,
+      getTodoListItems: notImplemented,
+      createTodoListItem: notImplemented,
+    }),
+    middleware: [genericErrorMiddleware],
+    port: {port: 3000, host: "127.0.0.1"},
+  })
+
+  console.info(`listening on http://${address.address}:${address.port}`)
+
+  process.on("SIGTERM", () => {
+    console.info("sigterm received, closing server")
+    server.close()
+  })
+}
+
+if (require.main === module) {
+  main().catch((err) => {
+    console.error("unhandled exception", err)
+    process.exit(1)
+  })
+}
diff --git a/packages/openapi-code-generator/src/core/input.ts b/packages/openapi-code-generator/src/core/input.ts
index 7aadbebec..873c9ff95 100644
--- a/packages/openapi-code-generator/src/core/input.ts
+++ b/packages/openapi-code-generator/src/core/input.ts
@@ -9,6 +9,7 @@ import type {
   RequestBody,
   Responses,
   Schema,
+  xInternalPreproccess,
 } from "./openapi-types"
 import type {
   IRModel,
@@ -20,6 +21,7 @@ import type {
   IRModelString,
   IROperation,
   IRParameter,
+  IRPreprocess,
   IRRef,
   IRResponse,
   MaybeIRModel,
@@ -195,6 +197,10 @@ export class Input {
     return normalizeSchemaObject(schema)
   }
 
+  preprocess(maybePreprocess: Reference | xInternalPreproccess): IRPreprocess {
+    return this.loader.preprocess(maybePreprocess)
+  }
+
   private normalizeRequestBodyObject(
     operationId: string,
     requestBody?: RequestBody | Reference,
@@ -368,6 +374,7 @@ function normalizeSchemaObject(
   const base: IRModelBase = {
     nullable: schemaObject.nullable || false,
     readOnly: schemaObject.readOnly || false,
+    "x-internal-preprocess": schemaObject["x-internal-preprocess"],
   }
 
   switch (schemaObject.type) {
diff --git a/packages/openapi-code-generator/src/core/openapi-loader.ts b/packages/openapi-code-generator/src/core/openapi-loader.ts
index e8c3c2960..3b2a1c8d9 100644
--- a/packages/openapi-code-generator/src/core/openapi-loader.ts
+++ b/packages/openapi-code-generator/src/core/openapi-loader.ts
@@ -14,6 +14,7 @@ import type {
   RequestBody,
   Response,
   Schema,
+  xInternalPreproccess,
 } from "./openapi-types"
 import {isRef} from "./openapi-utils"
 import type {OpenapiValidator} from "./openapi-validator"
@@ -73,6 +74,10 @@ export class OpenapiLoader {
     return isRef(maybeRef) ? this.$ref(maybeRef) : maybeRef
   }
 
+  preprocess(maybeRef: Reference | xInternalPreproccess): xInternalPreproccess {
+    return isRef(maybeRef) ? this.$ref(maybeRef) : maybeRef
+  }
+
   private $ref<T>({$ref}: Reference): T {
     const [key, objPath] = $ref.split("#")
 
diff --git a/packages/openapi-code-generator/src/core/openapi-types-normalized.ts b/packages/openapi-code-generator/src/core/openapi-types-normalized.ts
index da549f446..13668ae7c 100644
--- a/packages/openapi-code-generator/src/core/openapi-types-normalized.ts
+++ b/packages/openapi-code-generator/src/core/openapi-types-normalized.ts
@@ -1,6 +1,8 @@
+import {xInternalPreproccess} from "./openapi-types"
 import type {HttpMethod} from "./utils"
 
 export interface IRRef {
+  "x-internal-preprocess"?: MaybeIRPreprocess | undefined
   $ref: string
 }
 
@@ -8,6 +10,21 @@ export interface IRModelBase {
   // Note: meaningless for top level objects, maybe we can exclude these somehow in that case
   nullable: boolean /* false */
   readOnly: boolean /* false */
+
+  "x-internal-preprocess"?: MaybeIRPreprocess | undefined
+}
+
+export type MaybeIRPreprocess = IRPreprocess | IRRef
+
+export type IRPreprocess = {
+  serialize?: {
+    fn: string
+    type?: string
+  }
+  deserialize?: {
+    fn: string
+    type?: string
+  }
 }
 
 export type IRModelNumericFormat = "int32" | "int64" | "float" | "double"
diff --git a/packages/openapi-code-generator/src/core/openapi-types.ts b/packages/openapi-code-generator/src/core/openapi-types.ts
index bd4cef0ff..a81374db3 100644
--- a/packages/openapi-code-generator/src/core/openapi-types.ts
+++ b/packages/openapi-code-generator/src/core/openapi-types.ts
@@ -248,6 +248,19 @@ export interface Schema {
   externalDocs?: ExternalDocumentation | undefined
   deprecated?: boolean | undefined
   // xml?: XML | undefined
+
+  "x-internal-preprocess"?: xInternalPreproccess | Reference | undefined
+}
+
+export interface xInternalPreproccess {
+  serialize?: {
+    fn: string
+    type?: string
+  }
+  deserialize?: {
+    fn: string
+    type?: string
+  }
 }
 
 export interface Discriminator {
@@ -265,6 +278,7 @@ export interface Example {
 }
 
 export interface Reference {
+  "x-internal-preprocess"?: xInternalPreproccess | Reference | undefined
   $ref: string
 }
 
diff --git a/packages/openapi-code-generator/src/typescript/common/schema-builders/abstract-schema-builder.ts b/packages/openapi-code-generator/src/typescript/common/schema-builders/abstract-schema-builder.ts
index 4c30f120e..ac33275a6 100644
--- a/packages/openapi-code-generator/src/typescript/common/schema-builders/abstract-schema-builder.ts
+++ b/packages/openapi-code-generator/src/typescript/common/schema-builders/abstract-schema-builder.ts
@@ -163,7 +163,21 @@ export abstract class AbstractSchemaBuilder<
       if (parameter.required) {
         model.required.push(parameter.name)
       }
-      model.properties[parameter.name] = parameter.schema
+
+      const dereferenced = this.input.loader.schema(parameter.schema)
+
+      if (parameter.in === "query" && dereferenced.type === "array") {
+        model.properties[parameter.name] = {
+          ...parameter.schema,
+          "x-internal-preprocess": {
+            deserialize: {
+              fn: "(it: unknown) => Array.isArray(it) || it === undefined ? it : [it]",
+            },
+          },
+        }
+      } else {
+        model.properties[parameter.name] = parameter.schema
+      }
     }
 
     return this.fromModel(model, true, true)
@@ -192,6 +206,15 @@ export abstract class AbstractSchemaBuilder<
         result = this.nullable(result)
       }
 
+      if (maybeModel["x-internal-preprocess"]) {
+        const dereferenced = this.input.loader.preprocess(
+          maybeModel["x-internal-preprocess"],
+        )
+        if (dereferenced.deserialize) {
+          result = this.preprocess(result, dereferenced.deserialize.fn)
+        }
+      }
+
       result = required ? this.required(result) : this.optional(result)
 
       if (this.graph.circular.has(name) && !isAnonymous) {
@@ -298,6 +321,15 @@ export abstract class AbstractSchemaBuilder<
       }
     }
 
+    if (model["x-internal-preprocess"]) {
+      const dereferenced = this.input.loader.preprocess(
+        model["x-internal-preprocess"],
+      )
+      if (dereferenced.deserialize) {
+        result = this.preprocess(result, dereferenced.deserialize.fn)
+      }
+    }
+
     if (nullable || model.nullable) {
       result = this.nullable(result)
     }
@@ -327,6 +359,11 @@ export abstract class AbstractSchemaBuilder<
 
   protected abstract union(schemas: string[]): string
 
+  protected abstract preprocess(
+    schema: string,
+    transformation: string | ((it: unknown) => unknown),
+  ): string
+
   protected abstract nullable(schema: string): string
 
   protected abstract optional(schema: string): string
diff --git a/packages/openapi-code-generator/src/typescript/common/schema-builders/joi-schema-builder.ts b/packages/openapi-code-generator/src/typescript/common/schema-builders/joi-schema-builder.ts
index 837086ef1..db6c9f4be 100644
--- a/packages/openapi-code-generator/src/typescript/common/schema-builders/joi-schema-builder.ts
+++ b/packages/openapi-code-generator/src/typescript/common/schema-builders/joi-schema-builder.ts
@@ -108,6 +108,26 @@ export class JoiBuilder extends AbstractSchemaBuilder<
       .join(".")
   }
 
+  protected preprocess(
+    schema: string,
+    transformation: string | ((it: unknown) => unknown),
+  ) {
+    // TODO: yep this is horrid, but trying to create an extension like:
+    //       joi.extend({type: 'maybeArray', prepare: (it) => ({value: Array.isArray(it) || it === undefined ? it : [it]})})
+    //       doesn't appear to be chainable, so not sure where else to go, eg:
+    //       > custom.maybeArray().validate([1,2])
+    //       { value: [ 1, 2 ] }
+    //       > custom.maybeArray().validate(1)
+    //       { value: [ 1 ] }
+    //       > custom.maybeArray().array().items(custom.string()).validate([1,2])
+    //       Uncaught TypeError: custom.maybeArray(...).array is not a function
+    return `{
+      validate(it: unknown, opts: any) {
+        const transformation = ${transformation.toString()}
+        return ${schema}.validate(transformation(it), opts)}
+      }`
+  }
+
   protected nullable(schema: string): string {
     return [schema, "allow(null)"].join(".")
   }
diff --git a/packages/openapi-code-generator/src/typescript/common/schema-builders/zod-schema-builder.ts b/packages/openapi-code-generator/src/typescript/common/schema-builders/zod-schema-builder.ts
index 3876b3208..e125c4d58 100644
--- a/packages/openapi-code-generator/src/typescript/common/schema-builders/zod-schema-builder.ts
+++ b/packages/openapi-code-generator/src/typescript/common/schema-builders/zod-schema-builder.ts
@@ -133,6 +133,15 @@ export class ZodBuilder extends AbstractSchemaBuilder<
       .join(".")
   }
 
+  protected preprocess(
+    schema: string,
+    transformation: string | ((it: unknown) => unknown),
+  ) {
+    return [zod, `preprocess(${transformation.toString()}, ${schema})`]
+      .filter(isDefined)
+      .join(".")
+  }
+
   protected nullable(schema: string): string {
     return [schema, "nullable()"].filter(isDefined).join(".")
   }
diff --git a/packages/openapi-code-generator/src/typescript/typescript-koa/typescript-koa.generator.ts b/packages/openapi-code-generator/src/typescript/typescript-koa/typescript-koa.generator.ts
index 701a9cb87..ff290fc54 100644
--- a/packages/openapi-code-generator/src/typescript/typescript-koa/typescript-koa.generator.ts
+++ b/packages/openapi-code-generator/src/typescript/typescript-koa/typescript-koa.generator.ts
@@ -25,14 +25,14 @@ import {
 
 function reduceParamsToOpenApiSchema(parameters: IRParameter[]): IRModelObject {
   return parameters.reduce(
-    (acc, parameter) => {
-      acc.properties[parameter.name] = parameter.schema
+    (model, parameter) => {
+      model.properties[parameter.name] = parameter.schema
 
       if (parameter.required) {
-        acc.required.push(parameter.name)
+        model.required.push(parameter.name)
       }
 
-      return acc
+      return model
     },
     {
       type: "object",