Adding Slave Zone - Failed To Determine a Valid IP address For This System

Debian:
10:

Hello,

We setup a second Virtualmin as a secondary DNS slave. However when we add a new virtual server to the main Virtualmin (primary) system we always get a message:

Adding slave zone on second.virtualmin_system.com …
… failed to determine a valid IP address for this system (got 127.0.1.1). You will need to set the IP in the BIND DNS Server module.

I am not sure where I need to make this change. I presume it needs the public IP address but where?