Running it inside a container is the main thing here. WHMCS takes the internal ip of the container that it is running in and treats it like the public address that would be used for accessing the panel from the Internet. The workaround for the containerized IP address that I posted worked fine on whmcs v6, and as far as I remember, whmcs support gave us this solution when we asked them about it.
Doesn't the address have to match with the license number? I assume (the obvious) that you cannot use a license for more than one installation, so I don't understand your concerns here.