Errors

Every failing request answers with the same envelope:

{
  "error": {
    "code": "NOT_FOUND",
    "message": "human-readable description of what went wrong"
  }
}

Status	code
400	BAD_REQUEST
401	UNAUTHORIZED
403	FORBIDDEN
404	NOT_FOUND
409	CONFLICT
500	INTERNAL

Match on code — it is stable. message is written for humans and its wording is not part of the contract. details is present only where an error carries structured context, such as the resource a conflict collided with.