Every error is:
{"success": false, "error": "...", "code": "...", "details"?: [{"location", "message", "value"}]}codenames the cause;errordescribes it.detailslists each rejected value.
Each operation in the API reference lists the statuses it answers with and the codes behind each.
A path no endpoint has answers 404 ROUTE_NOT_FOUND, and a method the path does not take answers 405
METHOD_NOT_ALLOWED, with the allowed methods in Allow.