Offline geomap with custom mapserver not displaying basemap

I have a closed network with several computers. I have a map server (MapTiler) running on PC1, and my grafana server is on PC2. I can see the map server from any computer on my network, and have a geomap panel that is responding to my interactions, changing zoom/long/lat, and displays data layers as it should.

The problem is that the base layer itself is not displaying at all, no matter on which PC I’m working. I opened wireshark and apparently grafana is not making any requests to the map server.
I have a geomap panel configured to the correct address, with the necessary {z}/{x}/{y} variables in the URL.

Does the geomap panel need internet access for some reason?
*EDIT: Is it possible that this feature of offline maps is only available for Grafana Enterprise? All other features are working fine for me offline so far.