Validation failed or the request was malformed.

Missing or invalid credentials (API key or M2M JWT).

Authenticated, but the credential lacks the required scope.

The requested resource does not exist for this tenant.

Conflict — e.g. a duplicate external_ref or an idempotency-key clash.

Semantic validation error (the value is well-formed but not acceptable).

Rate limit exceeded — retry after the window resets.

Unexpected internal error. The request_id identifies the failure.