This is an optional status response type that the REST Catalog can issue when the token has expired. The client MAY request a new access token and retry the request. 401 UnauthorizedResponse SHOULD be preferred over this response type on token expiry.

The service is not ready to handle the request, request could have been partially processed.
The service may additionally send a Retry-After header to indicate when to retry, a non idempotent request should only be retried by the client when the Retry-After header is present.

A server-side problem that might not be addressable from the client side. Used for server 5xx errors without more specific documentation in individual routes.