For Wireguard on your iPhone, check if you have these two lines. If yes then it means wireguard server can be reached. If not then it means the server cannot be reached at all.
So, for your issue, first we need to make sure on your AXT1800 you do not have vpn client enabled. Otherwise it is vpn cascading and have to upgrade to firmware 4.1.1.
If you only have vpn server enabled, then next thing is to check if your public IP address (which is the endpoint in wireguard config) is accessible and it is fixed. If it is dynamic you may need to use ddns.