No audio on forwarded call

I have 2 offices connected by VPN. Each has a PBXdistro box.

I created 2 ring groups on each machine. The first ring group rings all the phones on the local PBX. If no answer, it is forwarded to the second ring group which dials the SIP trunk to the other location.

the problem is, a forwarded call cannot hear or be heard. It rings but nobody’s there.

If you pick a phone and dial the phone number to the other location there is no problem. If you dial an extension directly, there is no problem. Forwarded calls IS a problem.

Any help?