Hi Team, I’m reaching out regarding an urgent issue we’re encountering with the call transfer feature using SIP. We’ve configured a transfer tool (ID: 17b97721-a76d-4fb1-943c-f2e7a8e41f4e) with a SIP destination. However, every attempt to initiate a transfer results in a “call transfer failure” message (call details attached below), and we cannot identify the root cause. We have already whitelisted the required IPs on our PBX server, as outlined in Vapi’s documentation, but the issue persists. This problem is currently blocking our team and preventing us from serving our clients effectively. We would greatly appreciate your assistance in resolving this as soon as possible. Please let us know if you need any additional details from our side. **Call ID: 019dbfc4-224a-7000-83f5-e79519f85cbd,019dbfc3-1da8-7000-94df-30b35b5db820 Issue: Call transfer failure occurred. Expected: The assistant should transfer the call properly Browser: Chrome**

Hi, I can help you get this resolved quickly. From what you’ve described, this is likely happening at the SIP/PBX level rather than just the transfer tool itself usually related to how the PBX handles the transfer (REFER/INVITE) or how the SIP destination is configured. If you can share a failed call log or a quick screenshot of the SIP settings (you can mask sensitive info), I’ll trace exactly where it’s breaking and guide you to a fix right away. @AJ

hey @Praise Heritage Abayomi here is the log and snapshot of how the tool is setted up, please note the sip uri that you are seeing is a dummy one let me know if you need anything https://cdn.discordapp.com/attachments/1497237154840186930/1497268972867813568/Screenshot_2026-04-24_at_9.41.57_PM.png?ex=69ece7e5&is=69eb9665&hm=82b9453ed3f364869eb28c198436039ad3d0b6e568f0568ff55c0d63f34ea16b& https://cdn.discordapp.com/attachments/1497237154840186930/1497268973111345152/call-logs-2026-04-24T16-09-13-602Z.json?ex=69ece7e5&is=69eb9665&hm=97b6fd8ea2da6c5f4c9d012c31bb39e02246d962ba20aab83aaefb403fcfc0c6&

@AJ After going through the logs, the issue isn't the PBX or IP whitelisting it's the call type. This was a web call (Daily.co/WebRTC transport), and the transfer failed just 4ms after being initiated, meaning it never even reached the PBX. A real network or whitelist rejection would take several seconds. This points to Vapi dropping the transfer internally before any SIP packet was sent web-to-SIP transfers behave differently from phone-to-SIP. If it would help, I can jump in and resolve this directly.

hey @Praise Heritage Abayomi sharing a real ph call logs too please take a look to this https://cdn.discordapp.com/attachments/1497237154840186930/1497287244174856202/call-logs-2026-04-24T17-24-37-560Z.json?ex=69ecf8e9&is=69eba769&hm=026d03eab3fdd074b6c5e5d234c3e1b1bdf0baaf2875f46b42c22acdb1a4d2e7&

Hey AJ, apologies for the delayed response. It looks like you've resolved the issue. please let us know if you experience any issues with Vapi in the future, and we'll be happy to help. Thanks, Akash