How to turn off SIP ALG on a FortiGate firewall

Logon to your FortiGate’s console
Type ‘config system session-helper’ and press enter
Type ‘show’
Find the entry which shows ‘set name sip’ and note the ID (it’s usually 13)
Type ‘delete 13’ (or the number shown on your firewall) and then ‘end’
Type ‘config system settings’
Type ‘set default-voip-alg-mode kernel-helper-based’ and then ‘end’
Type ‘config voip profile’ then ‘edit default’
Type ‘config sip’ then ‘set status disable’
Type ‘end’ then ‘end’
Reboot the router