When the BOT attempts to transfer a call with Telnyx the call fails, but works with the twilio telephony integration.

The issue occurs because VAPI uses the SIP REFER method for call transfers, which Telnyx does not support—causing the transfer to fail. Telnyx support recommends eliminating SIP REFER on VAPI's end, but there is currently no documented way to change the SIP verb or transfer method in VAPI for Telnyx. At this time, there is no actionable workaround or configuration available to resolve this with Telnyx. You may need to contact VAPI support for further assistance or updates on this limitation. Source: - [Discord discussion on VAPI and Telnyx transfer issue](https://discord.com/channels/1211482211119796234/1343963959421829172)

Ensure proper SIP trunk setup, use correct API parameters, monitor Telnyx webhook events, and compare configurations with Twilio..

Thank you, this resolved the problem.

The main issue with VAPI call transfers on Telnyx is that VAPI uses the SIP REFER method, which Telnyx does not support for transfers. To troubleshoot, ensure your SIP trunk is set up correctly, use the correct API parameters, and compare your Telnyx configuration with your working Twilio setup. Monitoring Telnyx webhook events may also help identify where the transfer fails. If you continue to experience issues, contacting VAPI support for updates on SIP REFER alternatives is recommended. [See Discord discussion for more details](https://discord.com/channels/1211482211119796234/1343963959421829172) Source: - [Discord discussion on VAPI and Telnyx transfer issue](https://discord.com/channels/1211482211119796234/1343963959421829172)

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