Hello guys, no matter what I try whenever the assistant goes for a warm transfer; it says "allow me to put you on hold" then after 5 seconds it starts to ring for 10s and then ends the call then my operater recieves a call from the vapi assistant it stays at 00:00 after answering, and then call ends, no transfer occurs What could this be and how do i fix it?

It sounds like your warm transfer is failing because Vapi only supports warm transfers with Twilio-based telephony systems. If you are using a SIP provider like Plivo, warm transfers (especially those using SIP REFER) are not supported and will result in the behavior you described (call rings, then ends, operator sees 00:00 and disconnects). Actionable step: Switch your number to a Twilio phone number in Vapi for warm transfer support, or use blind transfer if you must stay with your current SIP provider. For reference:

json
"transferPlan": {
  "mode": "warm-transfer-experimental",
  // ... other required fields
}

Note: If you are already using Twilio and still see this issue, double-check your transferPlan configuration and ensure all required parameters are set correctly. [See more in the Vapi docs](https://docs.vapi.ai/call-forwarding) Sources: - [Call Forwarding](https://docs.vapi.ai/call-forwarding) - [Assistant-based warm transfer](https://docs.vapi.ai/calls/assistant-based-warm-transfer) - [Plivo SIP Integration](https://docs.vapi.ai/advanced/sip/plivo) - [Discord discussion: Warm transfers not working](https://discord.com/channels/1211482211119796234/1366650099035541544)

Hey, I can help you fix this. It sounds like the SIP transfer isn’t completing—possibly due to an invalid SIP response or missing media setup. Are you using a webhook or the built-in “Transfer Call” tool? If you can share the transfer logs or payload, I can pinpoint the issue faster. @halsey

Hi, could you please provide a call id where you experienced this issue? We would like to review the logs to identify the cause.