When I start the driver I get the following output:
GfxTablet driver (protocol version 1) is ready and listening on 0.0.0.0:40118 (UDP)
Hint: Make sure that this port is not blocked by your firewall.
How can I set the correct IP?
I had the same symptoms. Try the changes to the code I made in pull request 95. It uses a newer Linux API to register the device, and libinput seems happy with it now, so it works in gimp and inkscape.