Can't transfer FreePBX calls over VPN from Polycom phone using Fortinet firewalls.
We recently replaced our Cisco firewalls with Fortinet firewalls. The firewall at the site having the problem is a FortiGate 30D. The firewall at our main site is a FortiGate 70D. They are connected via Site to Site VPN. All traffic is allowed to pass between sites. We have a FreePBX Asterisk system at our main site (behind the 70D) and the phones there work just fine. However, we have a remote Polycom VVX410 at the site with the 30D which connects through the VPN to our FreePBX system. When that phone picks up an incoming call and tries to transfer it, the call gets stuck in a perpetual hold and it can no longer be accessed. That phone can also no longer see the BLF lights when other users are on the phone. These all worked prior to putting in the FortiGate.
I have disabled SIP-helper, sip-nat-trace and RTP on the FortiGate and reboot with no change. What can be done to get this phone working properly again?