A change line names a subcontract that is not for the order's job and phase and the line's vendor, or is not status 3, 4 or 5. 422. Nothing is written.
OPDC API error code
SUBCONTRACT_NOT_OPEN
HTTP status 422
The API answers with a problem document (RFC 9457) whose type is https://twinn.engineering/errors/subcontract-not-open, and with X-Error-Code: SUBCONTRACT_NOT_OPEN. Branch on the code, never on the detail text.