Help configuring a Grandstream UCM6200 series PBX with sip trunk service on a Sophos XG Firewall (SG210 Appliance) with SFOS 16.01.1

I have a Grandstream UCM6200 series PBX which I am trying to connect to a sip trunk provider.

I currently am able to make calls into the system from an outside US telephone number. I can also establish calls from the PBX to an outside number with the distinction that calls originating from my system do not have audio. Whereas calls from outside transmit audio both ways just fine.

I've tried a Business application rules per the documentation here: https://community.sophos.com/kb/en-us/122976

My SIP Provider functions a little differently than most. Please see the following brief information: http://support.siptrunk.com/hc/en-us/articles/208652806-I-Don-t-Have-Audio

I have another system like this configured at a different physical location, using an SG210 running the SG OS. It is working fine.

I'd appreciate any help to get this working.

Thank you!