One very bad practice that is quite common is using status codes in application specific ways and not including a standard error payload. One way to think of i

One very bad practice that is quite common is using status codes in application specific ways and not including a standard error payload. One way to think of it is that status codes are part of the transport, and your own application logic (validation, application error conditions, warnings, etc.) should never use HTTP error codes. A dumb proxy server should be able to cache any response (including its status code) on a GET or HEAD without needing to know about any application logic.