After configuring the UDP/TCP settings required by your PBX in the Virtual IP tab on your Fortinet device, the following commands must be executed from the CLI console to ensure voice packets are sent and received without issues.

Commands to run on the FortiGate CLI console
1. config system settings
set sip-helper disable
set sip-nat-trace disable
end
2.
config system session-helper
show “delete the line containing sip”
delete 12 (for example)
end
reboot fortigate