I guess that is more likely to be a problem with the web page thats doing the registration, or you actually are entering an invalid or in use DevEUI.
In TTN you dont configure for connection to a specific gateway, the node should connect to whichever gateway is nearest.
I see very little use of TTN on here, dont know if some of the paid support engineers keep an eye on whats happening on the public forums.
Thanks for your response. I have successfully added the sensors to a TTN application but they are not connecting to any gateway. In my zone, the only LoRaWAN gateway should be my Arduino Pro Gateway but the sensors don’t find that device.
However, as you can see in the image I attach, the gateway is up and running…