Help with the connection of a P-NUCELO-LRWAN2 gateway

Hi everyone,
I am pretty new to the LoRa world and I am trying to implement a network server on a Raspberry Pi 4 to read messages from a gateway. Since it seems that no raspberry pi hat is available, I went with the ST Microelectronics P-NUCELO-LRWAN2 discovery kit.

In a first instance, I tried to follow all the documentation provided by ST and I was successful in connecting the gateway to the Loriot Network Server. Since I am developing this for a client, I would like to host my network server and not rely on 3rd party servers.

I followed the documentation provided on the Chirpstack website and I also followed the setup using this video from mobilefish and the server seems to be up and running good, but on the GUI I cannot see the gateway.

The Chirpstack Gateway Bridge is mounted on the raspberry, with all the other components. I have tried to debug the problem following the gateway bridge documentation and everything seems to work, except that I have no log_file (but I can see the packet sent using journalctl -f -n 100 -u chirpstack-gateway-bridge).

I then switched to the Chipstack Network Server and in the log I find this error:

Mar 25 17:02:19 raspberrypi chirpstack-network-server[448]:
time="2020-03-25T17:02:19+01:00" level=error
msg="uplink: processing uplink frame error"
error="join-request to join-server error: response error,
 code: Other, description: get device-keys
 error: object does not exist"

This error is similar to the one reported in the documentation but I don’t get how to solve it. Do you have some hints on that?

Thank you in advance for your help!