I get a message saying that "GeoIP cannot function"

That means you have not synced the MaxMind GeoLite2 database yet.

Once Regular Labs GeoIP is installed for the first time on your site, you will be presented with a message saying that GeoIP cannot function until you sync the MaxMind GeoLite 2 database.

That is because MaxMind GeoLite2 requires you to create a free account (no purchase required) and create a License Key.

This means that in order to download the GeoIP database on your website, you first need to create a License Key and enter it in the GeoIP system plugin settings.