Hello VAPI community. I am stuck at transferring call from VAPI to Zadarma PBX. I have two virtual numbers, one is connected to the Zadarma PBX and forwards all calls to VAPI, the second, is connected to PBX and receives calls forwarded from VAPI. Zadarma states they do not accept

SIP REFER

, but they do

PREFER

. Here is my transferCall function

{
  "type": "transferCall",
  "destinations": [
    {
      "type": "sip",
      "sipUri": "sip:+97xxxxx@pbx.zadarma.com",
      "sipHeaders": {
        "Referred-By": "sip:+9xxxxx@sip.zadarma.com"
      }
    }
  ]
}

On the PBX, the transferred calls are "always" forwarded to my local number

+912xxxx

This successfully lands the transferred call to the PBX according to the logs but nothing happens afterwards. It rings and terminates. [Attached] - Zadarma team had shared a sample of PREFER, I don't know what I miss in my setup. Anyone with a clue or experience on this please share. Thank you. https://cdn.discordapp.com/attachments/1211484481848873020/1395767621843947540/PREFER.png?ex=687ba565&is=687a53e5&hm=bdba575885e939eb5cadc1e685c227870c2550672bf665d14c52ccff083666eb&