iOS cannot reach to other devices in tailscale

I have created a tailscale network. I have added four devices so far. They are windows, macOS, ubuntu and iPhone. All devices work perfectly and they ping each other but my iPhone does not work.

When I run tailscale client on iOS it lists other three devices. I click the up left button and it becomes activated after a while, but I cannot ping other devices. The exit node also does not work on iOS, when I use the exit node, which is the ubuntu device in my case, it losses the internet connection.

The windows and the macOS can use the ubuntu station as an exit node without any problems, so I think that the problem is the iOS, not the ubuntu server.

Please help to resolve the issue.
Thanks