Note that as this process may temporarily interrupt your internet connection and phone service, we recommend doing this in an off-peak period or outside of business hours.
Learn more about SIP ALG in our knowledge base article here: SIP ALG
Disabling SIP ALG
From the router's menu, click Advanced
From the left navigation menu, select Firewall Settings
Under Application Level Gateway (ALG) Configuration, disable SIP
Click save and, if prompted, restart your router.