You received a 401, then sent another request to the server — why is this needed?

The 401 Unauthorized response code indicates that the request requires authentication or the provided authentication data is invalid. If you send another request after receiving a 401, it usually involves attempting to refresh or obtain a new access token (for example, via a refresh token) and then retrying the request with the correct credentials. This approach is necessary for seamless user session recovery without requiring user intervention.

Example: When working with an API, if the access token expires, the client receives a 401, then automatically sends a request to refresh the token, obtains a new access token, and repeats the original request with the new token.