Wireguard client not connecting

I've set up Wireguard server on GL X3000 Spitz. All seems OK. I've installed the WG client from WG website on my Android phone and all seems OK. I've created a profile on the X3000 for the WG client and got a .conf file. I've also created a config using the scan QR code method. I've set up a tunnel on the phone using the file and all the details look OK - keys, DNS, port etc.
But when I start tunnel it does not connect.
Any ideas?

Do you use the X3000 with cellular internet?

If yes: You will be behind CGNAT and not able to host a server.

Yes. Thanks for that.
Tom

PS how can I tell I'm behind CGNAT and is there a way round it?

Mostly experience.

Consumer internet via cellular, coax and StarLink is mostly CGNAT.