4xx is a client error and 429 indicates that particular client is making too many requests. 5xx is a server error and 503 says the service itself is unavailable

4xx is a client error and 429 indicates that particular client is making too many requests. 5xx is a server error and 503 says the service itself is unavailable irrespective of the client’s actions. In this particular case it’d be unavailable for contractual rather than technical reasons, but it’s still the right status