I want to use Syncthing on my mobile phone so I can sync my photos on the move.
What I noticed is that while syncthing connects and works well. When I am connected via tailscale, I cannot connect to any of my self-hosted URLS.
These are reachable via my 4G connection when Tailscale is not active.
I am not sure what I need to do to be able to resolve to these URLs when Tailscale is connected.
You can use your own internal DNS servers with Tailscale and there is a domain override option as well.
Thanks for that. When and added DNS settings but still no joy. I then needed to travel abroad and was having issues with the plane wifi on my phone. In going through the settings I saw that I had added a private DNS ages ago and on the phone and herein lay the issue 
Removed that setting and all is well again