I can pass the Echo Test, but the internal extension communication will hang up when connected with message: Normal Remote hang up by Zoipher. I am success to talk before. I don’t know whether the Extension settings or Zoipher settings has problem!
would probably be a good place to start. Examine the logs and see if you can see a problem with the connections. You may also need to add some SIP debugging (based on your current SIP Channel Driver).