@khalezin I'm sorry to hear that you're experiencing issues with the transferCall tool. To assist you better, could you please provide more details about the problem? Specifically, are you receiving any error messages when you attempt to use the transferCall tool, or is the call simply not being transferred as expected? Additionally, could you confirm if you have specified the destinations to which the calls should be transferred, or if you are relying on the server.url to obtain the transfer destination?

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This is the request on twilio side for this call https://dashboard.vapi.ai/calls/ad12137e-83eb-4af6-9c83-c2aaae0543b0 https://cdn.discordapp.com/attachments/1315957501845442570/1316077837551407135/2024-12-10_19-22.png?ex=6759bc80&is=67586b00&hm=add7b2b4454de0643279e64b5837c0c54f733417e98f9a7754ffea601138cf64&

This is the answer from twilio support

Hello Dmitrii, 
 
Thanks for contacting Twilio Technical Support. My name is Pritam, I will be assisting you with this case.
 
I have checked the given sample and can see that you have tried to update the call but received 21220 error, which primarily means You attempted a realtime operation on a Call that was not in-progress. Calls that have completed cannot be recorded or redirected.
 
Further I have checked, can see that you have tried to update the call using API, at the same time you have sent <Hangup> in that same request, as a result call got disconnected and error code 21220 triggered.