Twilio cold transfer not working

After doing all 4 suggested checks and changes the transfer is still not working.
Please check this call ID

call_31b0c696b9ba2f994c366ffc7c0

This is the call log from twilio

We used to recieve a refer callback whenever a transfer was initiated. We don’t recieve it anymore.

this is our /refer endpoint.

        payload = dict(request.POST)
        refer_transfer_target = (payload.get("ReferTransferTarget") or [None])[0]
        dial_type, dial_target = self._normalize_refer_transfer_target(
            refer_transfer_target
        )

        voice_response = VoiceResponse()
        if dial_type and dial_target:
            dial = Dial()
            if dial_type == "sip":
                dial.sip(dial_target)
            else:
                dial.number(dial_target)
            voice_response.append(dial)