No Audio or One Way Audio after Transfer or Forwarding Print

Symptom

When you perform the attended-transfer(particularly the SIP REFER method)  by the transfer button on the IP phone. After the transfer the call, it would have the one-way audio or no audio on both sides for the caller and the transfer target party.

Or the incoming call is forwarded by the extension always forwarding settings.

Solution

Try to disable the Allow RTP Re-Invite option in the SIP Advanced setting.