While both return unauthorized access, a 401 (Unauthorized) indicates the credentials are wrong, while a 403 (Forbidden) means the credentials are correct, but the user doesn't have permission to access the resource. A 401 requires the user to re-authenticate, whereas a 403 means the access is permanently denied.

A 401 Unauthorized error indicates that the client's credentials are invalid, while a 403 Forbidden error indicates that the client is authenticated but lacks the necessary permissions to access the requested resource. The server returns a 401 when the authentication is incorrect, and a 403 when the authentication is correct but access is denied.