Why does a 401 error code occur using application token ? and I have been following the instructions in miscrosoft documentation

[AngGaGim]

code:

async def get_user_messages():
    messages = await (client.users.by_user_id("763b2b29-a5e8-4088-bac7-7e84e982c01f").messages.get())
    if messages and messages.value:
        for msg in messages.value:
            # print(msg)
            print(msg.subject, msg.id, msg.from_)
            
await get_user_messages()

exception:

---------------------------------------------------------------------------
APIError                                  Traceback (most recent call last)
Cell In[100], line 8
      4         for msg in messages.value:
      5             # print(msg)
      6             print(msg.subject, msg.id, msg.from_)
----> 8 await get_user_messages()

Cell In[100], line 2, in get_user_messages()
      1 async def get_user_messages():
----> 2     messages = await (client.users.by_user_id("763b2b29-a5e8-4088-bac7-7e84e982c01f").messages.get())
      3     if messages and messages.value:
      4         for msg in messages.value:
      5             # print(msg)

File ~/my-python-projects/outlook-qa/.venv/lib/python3.11/site-packages/msgraph/generated/users/item/messages/messages_request_builder.py:69, in MessagesRequestBuilder.get(self, request_configuration)
     66     raise Exception("Http core is null") 
     67 from ....models.message_collection_response import MessageCollectionResponse
---> 69 return await self.request_adapter.send_async(request_info, MessageCollectionResponse, error_mapping)

File ~/my-python-projects/outlook-qa/.venv/lib/python3.11/site-packages/kiota_http/httpx_request_adapter.py:193, in HttpxRequestAdapter.send_async(self, request_info, parsable_factory, error_map)
    190     parent_span.add_event(RESPONSE_HANDLER_EVENT_INVOKED_KEY)
    191     return await response_handler.handle_response_async(response, error_map)
--> 193 await self.throw_failed_responses(response, error_map, parent_span, parent_span)
    194 if self._should_return_none(response):
    195     return None

File ~/my-python-projects/outlook-qa/.venv/lib/python3.11/site-packages/kiota_http/httpx_request_adapter.py:575, in HttpxRequestAdapter.throw_failed_responses(self, response, error_map, parent_span, attribute_span)
    566     else:
    567         exc = APIError(
    568             (
    569                 "The server returned an unexpected status code and the error registered"
   (...)    573             response_headers,  # type: ignore
    574         )
--> 575     raise exc
    576 finally:
    577     _throw_failed_resp_span.end()

APIError: 
        APIError
        Code: 401
        message: The server returned an unexpected status code and the error registered for this code failed to deserialize: <class 'NoneType'>

The following codr is normal, I can get the users list of app:

from msgraph import GraphServiceClient
from azure.identity import ClientSecretCredential
async def get_user_id():
    scopes = ['https://graph.microsoft.com/.default']
    
    # azure.identity.aio
    credential = ClientSecretCredential(
        tenant_id=tenant_id,
        client_id=client_id,
        client_secret=client_secret)
    
    graph_client = GraphServiceClient(credential, scopes) # type: ignore
    # token = credential.get_token_info(scopes[0])
    result = await graph_client.users.get()
    return result

result = await get_user_id()