Reserve the 418 status code
Many API developers misuse/overload HTTP status codes when they should actually be using application specific status codes delivered via a wrapper to the response.Any time an API returns a correct response the HTTP response code should be 2xx.  Many developers use 4xx status codes to indicate things like data validation errors or other things that are not part of the HTTP transport.HTTP is the transport layer, and any application specific scenarios are best handled with a custom error namespace that can be returned within any 2xx HTTP response.Generally speaking, if the HTTP layer is returning 5xx you have a server problem and client code should not know anything about that or do anything but retry.  If the HTTP layer is returning 4xx then the client is likely poorly designed or misconfigured.But for typical client operation, when there is no server error or client design/configuration error, HTTP responses should be 2xx or 3xx and any additional detail should be handled in an application-specific way, not by overloading the meaning of HTTP response codes, which are for transport-related concerns only.