The integration technology used is called LightHouse Apps.
The MFD integration is compatible with the Axiom, Axiom Pro and Axiom XL MFDs running on LightHouse 3. The eS & gS Series multifunction displays which have been upgraded to LightHouse 3 are not compatible.
Raymarine MFDs need at least LightHouse v3.11 for compatibility, which was released in November 2019.
The MFD needs to be connected to the GX device using ethernet. It is not possible to connect over Wi-Fi. For the ethernet connection, a RayNet adapter is required.
The RayNet adapters can be purchased from Raymarine:
On the Victron GX Device, go to Settings → Services, and there enable MQTT.
Next, go to Settings → System Setup → Scroll to the bottom → Battery measurements. And there set up what batteries you want to see on the MFD; and by what name.
No other settings, such as IP addresses or similar are required, since the Axiom MFDs have an integrated DHCP server.
This video explains how to setup multiple battery measurements, and naming them.