File attachments are not turned on for this API key, or its setting could not be checked. 403. A Twinn administrator turns them on for the key. Nothing is stored or written.
OPDC API error code
ATTACHMENTS_DISABLED
HTTP status 403
The API answers with a problem document (RFC 9457) whose type is https://twinn.engineering/errors/attachments-disabled, and with X-Error-Code: ATTACHMENTS_DISABLED. Branch on the code, never on the detail text.