diff --git a/sandbox/data/examples/errors/responses/bad-gateway.json b/sandbox/data/examples/errors/responses/bad-gateway.json
new file mode 100644
index 00000000..a125f860
--- /dev/null
+++ b/sandbox/data/examples/errors/responses/bad-gateway.json
@@ -0,0 +1,3 @@
+{
+  "message": "Bad Gateway"
+}
diff --git a/sandbox/data/examples/errors/responses/tooManyRequests.json b/sandbox/data/examples/errors/responses/tooManyRequests.json
index 4babbd7d..36411d71 100644
--- a/sandbox/data/examples/errors/responses/tooManyRequests.json
+++ b/sandbox/data/examples/errors/responses/tooManyRequests.json
@@ -1,14 +1,10 @@
 {
-  "errors": [
-    {
-      "code": "NOTIFY_QUOTA",
-      "detail": "You have made too many requests. Please try again later.",
-      "id": "rrt-1931948104716186917-c-geu2-10664-3111479-3.0",
-      "links": {
-        "about": "https://digital.nhs.uk/developer/api-catalogue/nhs-notify-supplier"
-      },
-      "status": "429",
-      "title": "Too many requests"
-    }
-  ]
+  "interval": 1,
+  "limit": 1,
+  "message": "Your application, Notify-Supplier-App-Restricted - Internal Dev 2, has exceeded its quota of 1 requests every 1 minute(s) and is being rate limited.",
+  "message_id": "rrt-4773181658036170775-c-geu2-321623-73628915-2",
+  "policy": "quota",
+  "ratelimiting_expiry_time_ms": 1765372560000,
+  "scope": "application",
+  "timeunit": "minute"
 }
diff --git a/specification/api/components/endpoints/createMI.yml b/specification/api/components/endpoints/createMI.yml
index 04ee8664..0032ae07 100644
--- a/specification/api/components/endpoints/createMI.yml
+++ b/specification/api/components/endpoints/createMI.yml
@@ -15,3 +15,5 @@ responses:
     $ref: "../responses/errors/tooManyRequests.yml"
   '500':
     $ref: "../responses/errors/serverError.yml"
+  '502':
+    $ref: "../responses/errors/badGateway.yml"
diff --git a/specification/api/components/endpoints/getDataId.yml b/specification/api/components/endpoints/getDataId.yml
index c7574df4..1c5aef45 100644
--- a/specification/api/components/endpoints/getDataId.yml
+++ b/specification/api/components/endpoints/getDataId.yml
@@ -13,3 +13,5 @@ responses:
     $ref: "../responses/errors/tooManyRequests.yml"
   "500":
     $ref: "../responses/errors/serverError.yml"
+  "502":
+    $ref: "../responses/errors/badGateway.yml"
diff --git a/specification/api/components/endpoints/getLetterStatus.yml b/specification/api/components/endpoints/getLetterStatus.yml
index bee57b46..a7290dcf 100644
--- a/specification/api/components/endpoints/getLetterStatus.yml
+++ b/specification/api/components/endpoints/getLetterStatus.yml
@@ -11,5 +11,7 @@ responses:
     $ref: "../responses/errors/tooManyRequests.yml"
   "500":
     $ref: "../responses/errors/serverError.yml"
+  "502":
+    $ref: "../responses/errors/badGateway.yml"
 tags:
   - letter
diff --git a/specification/api/components/endpoints/listLetters.yml b/specification/api/components/endpoints/listLetters.yml
index 2d300c65..638f3917 100644
--- a/specification/api/components/endpoints/listLetters.yml
+++ b/specification/api/components/endpoints/listLetters.yml
@@ -18,3 +18,5 @@ responses:
     $ref: "../responses/errors/tooManyRequests.yml"
   '500':
     $ref: "../responses/errors/serverError.yml"
+  '502':
+    $ref: "../responses/errors/badGateway.yml"
diff --git a/specification/api/components/endpoints/patchLetter.yml b/specification/api/components/endpoints/patchLetter.yml
index 7e8775e2..61ba6dad 100644
--- a/specification/api/components/endpoints/patchLetter.yml
+++ b/specification/api/components/endpoints/patchLetter.yml
@@ -15,5 +15,7 @@ responses:
     $ref: "../responses/errors/tooManyRequests.yml"
   "500":
     $ref: "../responses/errors/serverError.yml"
+  "502":
+    $ref: "../responses/errors/badGateway.yml"
 tags:
   - letter
diff --git a/specification/api/components/endpoints/postLetters.yml b/specification/api/components/endpoints/postLetters.yml
index 4aeee72a..876c7fd1 100644
--- a/specification/api/components/endpoints/postLetters.yml
+++ b/specification/api/components/endpoints/postLetters.yml
@@ -15,3 +15,5 @@ responses:
     $ref: "../responses/errors/tooManyRequests.yml"
   '500':
     $ref: "../responses/errors/serverError.yml"
+  '502':
+    $ref: "../responses/errors/badGateway.yml"
diff --git a/specification/api/components/responses/errors/badGateway.yml b/specification/api/components/responses/errors/badGateway.yml
new file mode 100644
index 00000000..3d1cce78
--- /dev/null
+++ b/specification/api/components/responses/errors/badGateway.yml
@@ -0,0 +1,8 @@
+description: "Bad gateway"
+content:
+  application/vnd.api+json:
+    schema:
+      $ref: "../../schemas/apiGatewayError.yml"
+    examples:
+      error-bad-request:
+        $ref: ../../examples/errors/responses/bad-gateway.json
diff --git a/specification/api/components/responses/errors/tooManyRequests.yml b/specification/api/components/responses/errors/tooManyRequests.yml
index 292735e5..86aec81b 100644
--- a/specification/api/components/responses/errors/tooManyRequests.yml
+++ b/specification/api/components/responses/errors/tooManyRequests.yml
@@ -1,8 +1,33 @@
 description: Too many requests
 content:
-  application/vnd.api+json:
+  application/json:
     schema:
-      $ref: "../../schemas/errorResponse.yml"
+      type: object
+      properties:
+        message:
+          type: string
+          example: "Your application has exceeded its quota"
+        scope:
+          type: string
+          example: "application"
+        policy:
+          type: string
+          example: "quota"
+        limit:
+          type: integer
+          example: 300
+        interval:
+          type: integer
+          example: 1
+        timeunit:
+          type: string
+          example: "minute"
+        ratelimiting_expiry_time_ms:
+          type: integer
+          example: 1625498765123
+        message_id:
+          type: string
+          example: "rrt-4773181658036170775-c-geu2-321623-73628915-2"
     examples:
       error-too-many-requests:
         $ref: ../../examples/errors/responses/tooManyRequests.json
diff --git a/specification/api/components/schemas/apiGatewayError.yml b/specification/api/components/schemas/apiGatewayError.yml
new file mode 100644
index 00000000..a36048f6
--- /dev/null
+++ b/specification/api/components/schemas/apiGatewayError.yml
@@ -0,0 +1,9 @@
+description: API gateway error response
+content:
+  application/json:
+    schema:
+      type: object
+      properties:
+        message:
+          type: string
+          example: "Bad Gateway"