HTTP status codes / 4xx — Client error
401 Unauthorized
What it means
Authentication is missing or invalid — the server does not know who you are. (Misnamed: it is about authentication, not authorization; that is 403.)
What causes it
Missing/expired/malformed token or session, wrong API key, credentials sent to the wrong header.
How to fix it
Re-authenticate and check the Authorization header format (Bearer prefix, unexpired token). Check the WWW-Authenticate response header for what scheme the server expects.