(AccessDenied) when calling the AssumeRole operation

[tenbasetom]

Describe the bug
Upon running the script below, I got this error:

Traceback (most recent call last):
  File "/path/to/project/lib/python3.8/site-packages/cachetools/__init__.py", line 68, in __getitem__
    return self.__data[key]
KeyError: 'role_d628c45d0b65e289e3bc9ec298d1c7c0'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/path/to/project/lib/python3.8/site-packages/sp_api/base/client.py", line 112, in role
    role = role_cache[cache_key]
  File "/path/to/project/lib/python3.8/site-packages/cachetools/__init__.py", line 418, in __getitem__
    return cache_getitem(self, key)
  File "/path/to/project/lib/python3.8/site-packages/cachetools/__init__.py", line 70, in __getitem__
    return self.__missing__(key)
  File "/path/to/project/lib/python3.8/site-packages/cachetools/__init__.py", line 97, in __missing__
    raise KeyError(key)
KeyError: 'role_d628c45d0b65e289e3bc9ec298d1c7c0'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "test.py", line 14, in <module>
    order = order_client.get_order('113-4849434-1328255')
  File "/path/to/project/lib/python3.8/site-packages/sp_api/base/helpers.py", line 21, in wrapper
    return function(*args, **kwargs)
  File "/path/to/project/lib/python3.8/site-packages/sp_api/api/orders/orders.py", line 95, in get_order
    return self._request(fill_query_params(kwargs.pop('path'), order_id), params={**kwargs}, add_marketplace=False)
  File "/path/to/project/lib/python3.8/site-packages/sp_api/base/client.py", line 153, in _request
    auth=self._sign_request(),
  File "/path/to/project/lib/python3.8/site-packages/sp_api/base/client.py", line 122, in _sign_request
    role = self.role
  File "/path/to/project/lib/python3.8/site-packages/sp_api/base/client.py", line 114, in role
    role = self.set_role(cache_key)
  File "/path/to/project/lib/python3.8/site-packages/sp_api/base/client.py", line 81, in set_role
    role = self.boto3_client.assume_role(
  File "/path/to/project/lib/python3.8/site-packages/botocore/client.py", line 530, in _api_call
    return self._make_api_call(operation_name, kwargs)
  File "/path/to/project/lib/python3.8/site-packages/botocore/client.py", line 960, in _make_api_call
    raise error_class(parsed_response, operation_name)
botocore.exceptions.ClientError: An error occurred (AccessDenied) when calling the AssumeRole operation: Roles may not be assumed by root accounts.

test.py

from sp_api.base import Marketplaces
from sp_api.api import Orders

credentials = dict( ... )

order_client = Orders(credentials=credentials)
order = order_client.get_order('...')
print(order)

To Reproduce

Steps to reproduce the behavior:

1. Follow steps 1-5 at https://developer-docs.amazon.com/sp-api/docs/creating-and-configuring-iam-policies-and-entities
2. Create test.py (see code above)
3. Execute python test.py

Expected behavior

I expected to see a printout of the order data.

Desktop (please complete the following information):

• OS: Linux (Ubuntu 20.04.3)

Additional context

Python 3.8.10