Yeah I always feel incredibly dumb when I have to edit them. It’s also the only thing I could think of that might be causing issue with OPs tailnet.

Firstly, what type of things are you trying to allow your friend to do on your tailnet? I’ve had trouble in the past trying to get friends to connect to game servers across tailnets, but have been fine connecting friends to things like Jellyfin. Any information on this might be helpful to look over.

Secondly, Have you checked out the ACLs? Access controls to your network can sometimes make things not play nice. Here is the docs on managing your Access control list.