Hello. Are calls via zadarma trunk can be forwarded to another number (external) or SIP with SIP refer only? In your instruction guides I've found this method: SIP REFER (call transfer) If you need to transfer a call to another number, you will need to add a SIP Transfer based call forwarding where the transfer number will look like this: sip:transfer-number@your-telecom-provider-domain.com Example: sip:15557654321@sip.zadarma.com Unfortunately, it doesn't work, I've checked .pcap of calls during the transfer, the method is not supported (501), the calls are being dropped on zadarma side, and there is no option to activate the method within zadarma. protosartos — 00:13 Do you have any other solutions? Should I set the transfer somehow differently? The objective: to forward incoming calls from AI assistant to a human (external number) or SIP authorized device

Zadarma does not support SIP REFER to external numbers, so to forward calls from [Vapi](http://Vapi.ai) to a human PSTN or SIP, you should use Zadarma’s call forwarding for inbound routing and handle all call transfers like to external numbers or SIP devices within [Vapi](http://Vapi.ai) using its

transferCall

tool and SIP trunk setup..