I am investigating a persistent routing failure regarding SIP REFER methods on our BYOC Premises trunks. When our Architect flows attempt a blind transfer to an external PSTN number, the edge server transmits a SIP REFER to our Session Border Controller. However, the SIP trace indicates that the Replaces header within the Refer-To URI is malformed, causing our SBC to reject the transfer with a 400 Bad Request response. Consequently, the call disconnects instead of transferring. I have reviewed the Python SDK documentation and the platform API endpoints for trunk configuration, but I am unable to locate a setting to modify or disable the Replaces header generation on blind transfers. How can I resolve this malformed header issue?
Greetings. I have navigated this precise interoperability challenge when integrating external systems through our session border controllers. The issue you describe is rooted in how the Genesys Cloud Edge constructs the SIP REFER message during a blind transfer from an Architect flow.
By default, the Edge includes the Replaces header to ensure seamless call leg replacement. However, certain legacy SBCs strictly parse the Refer-To URI and will reject unexpected parameters.
To resolve this, you must access the external trunk settings within the Telephony configuration. Navigate to the ‘SIP Access Control’ section and modify the ‘Protocol’ properties.
You will find an option to disable ‘Send REFER’. When disabled, the Edge will utilize a SIP INVITE instead of a REFER for external transfers, completely bypassing the malformed header issue.
Hello. Adding to the previous response, we experienced this exact scenario during our migration from PureConnect. The PureConnect architecture handled SIP REFER messages differently, and our existing gateways were not prepared for the Genesys Cloud formatting.
If your organizational architecture requires you to utilize the REFER method rather than falling back to an INVITE, you will need to implement a SIP manipulation rule directly on your Session Border Controller. You can create a normalization script on the SBC to strip the Replaces header from the Refer-To URI before the message is routed to the PSTN provider.
This allows you to maintain the standard Genesys Cloud trunk configuration while ensuring compatibility with your downstream carriers.