Errors

The API uses standard HTTP status codes. The body of a failed response carries a single field, error, whose text describes the cause:

{ "error": "Invalid API key" }

That message is written for the developer, not for the end user: it may change, so it must never be used as a test value. Branch your logic on the status code.

Codes returned

Status	Cause	What to do
400	Invalid body or parameter	Fix the request; retrying it unchanged will fail again
401	Key missing, unknown or revoked	Check the X-API-Key header
403	Valid key without the required right, or called from an unauthorised IP	Check the key's scope and IP restriction
404	Resource does not exist, or belongs to another account	Do not tell the two apart: the answer is identical on purpose
429	Request ceiling reached	Wait, then retry with a backoff
500	Incident on the Metaventus side	Retry after a few seconds; if it persists, contact us

What the API does not do

A 404 on another account's resource is indistinguishable from a 404 on a resource that does not exist. That is deliberate: confirming that an identifier you do not own exists would leak information.

Any 2xx other than 200 is still a success. 201 signals a creation, 202 a request accepted whose processing continues in the background, 204 an operation that succeeded with no response body. Treating "not 200" as a failure is the most common integration mistake.