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 Licence Key. Current credentials also require your MaxMind Account ID; legacy Licence Key-only credentials remain supported.
This means that in order to download the GeoIP database on your website, you first need to enter the MaxMind Account ID and Licence Key in the GeoIP system plugin settings.