Looks like I got it working, just followed the guide on https://docs.pycom.io/tutorials/expansionboards/pygate/ with a few modifications.
Create a gateway in the v3 console
Download the Global configuration from the gateway overview page in the console
Add the gateway_ID stuff to the bottom of the downloaded global_conf.json file
Change downloaded global_conf.json to config.json
Add a Gateway EUI in the console, I used the GPy´s mac address and added ff:fe in the middle to avoid using a semi random that might conflict with an other gateway later on.
Use the Gateway EUI (not the human readable Gateway ID from console) as the gateway_ID in the config.json
Reboot and it seems to be working
Hope this makes sense