POST /api/prior-auth/requests/{request_id}/submit
``` Submission channel priority (per):
```text
EPA_API → CLEARINGHOUSE → PORTAL → FAX → MANUAL
``` The selected channel is included in the response. Payer webhook responses arrive at `POST /api/prior-auth/webhooks/payer-response` (HMAC-verified per payer secret).
Submit
POST /api/prior-auth/requests/{id}/submit
Submit a PA