unet multiplayer match not appearing

Hello,

I have implemented a multiplayer game, I have tested it on multiple devices (between Android phones and PC's) and everything works great.

I have set my phone to use data instead of WiFi just to check the internet part of it worked and it all seems to work.

I then gave the apk to a friend in another country to test it further, however none of the active matches appear on the list for them.

I cant see any games they create either.

Does anyone know why this might be happening?