Errors
Every failure is a JSON object with a code and a sentence. The sentence never echoes your key or your records.
The shape
{ "error": { "code": "insufficient_scope", "message": "…" } }. 401 means the key is missing, unknown, revoked or expired. 403 means the key or the shop may not do that. 422 means the body is not valid. 429 means you have used the minute's requests.