Asterisk issues / assume NAT problem, need help

The Asterisk/FreePBX server is in our data center behind our firewall. It’s on a network. Our telephones are at a remote site that has an IPSEC tunnel to the data center. These devices are on a network.

Calls between the phones at the remote sites work. Calls from our remote site to an extension on our Asterisk server (Directory for example) do not work; calls via our SIP trunk provider configured on the Asterisk server also do not work - there is no audio.

I’m sure this is a beginner NAT issue; I’m looking for guidance on how to resolve.

No NAT needed in that environment, check SIP settings localnet