Every error is:

json
{"success": false, "error": "...", "code": "...", "details"?: [{"location", "message", "value"}]}
  • code names the cause; error describes it.
  • details lists 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.