How to get Dedi app to work?

[olahaldor]

A friend and I have set up a server on a spare PC of his.
All is fine, both of us and a couple other friends can both join the game and the website, but we cannot get the dedi app to work, except for my friend who is on the same network as the server.

In the Settings > Miscellaneous page it says this error
Private local area network (LAN) address detected. Web API probably inaccessible from internet.

The links below that line for the map and other stuff, points to his local IP, so something is up. I just can't tell where to set things correctly so we can get the data accessible from outside.

Is there a file to switch something on? Is there a port that needs to be forwarded? A specific setting etc in a file?

We're going nuts about this. It's literally the only thing we need to figure out, and we're all set to enjoy the game to its full potential.