Create a rule for a specific external IP so there is no filtering

Hi Everyone,

We've had an intermittent issue with our software VOIP/SIP clients on our LAN having only one way audio.  Basically, when someone externally calls one of our internal users, the internal user can not hear the external users voice but the external caller can hear our internal office users voice.

I've unloaded the sip module as referenced in other posts, but we're still seeing the issue.

I'm running Sophos XG v18.

I'm looking for help on how to create a rule to the VOIP providers IP so there is no filtering whatsoever. 

Basically, I'm trusting their IP implicitly so we can test to see if it is something with our Sophos XG that is causing this issue.  It's one of those situations where the vendor is saying that it's our firewall that's creating the issue and we need to rule out any filtering by the firewall.

Any help would be appreciated.

Cheers,

Rick