We are running into an issue where the sip.dial block in Architect does not forward custom SIP headers to the external PBX during a blind transfer. The environment uses BYOC trunks in AWS US-East-1 with TLS 1.2. The flow works for initial dial but after the transfer executes, the remote party rejects the INVITE because the X-Customer-ID header is missing. I have verified the header definition in the Trunk settings and confirmed the values populate correctly in the flow variables before the block executes. Flow version is 1423. Is there a specific configuration required to persist custom headers through the transfer leg?
This behavior occurs when the transfer target does not match the original trunk profile. Check the sip.dial parameters for the headers object in the flow definition. You need to explicitly pass the header map to the second dial operation.
The API endpoint /api/v2/outbound/profiles also validates these settings. Try updating the trunk configuration at /api/v2/sip/trunks/{id} to allow custom headers on all legs.
This situation impacts business continuity if the header is required for downstream routing. We implemented a fallback flow using sip.dial with explicit priority settings. Ensure your Disaster Recovery plan accounts for this header dependency.
Testing in the sandbox environment helps validate header propagation before production deployment.