What is the difference between an MC 403 and an MC 401 error on Android?

MC 401 (Unauthorized) means the request requires authentication, but either no credentials were provided, or the provided credentials are invalid. MC 403 (Forbidden) means the server understands the request and the user is authenticated, but doesn't have permission to access the requested resource. 401 is about *who* you are, 403 is about *what* you're allowed to do.