Hello Jonathan,
You can find the url to your site in settings, not sure if that's what you need. If it isn't working in the mobile app, can you check that you're using the same network as for visiting the site? I don't know the specifics of your situation, but sometimes with this kind of network restrictions the mobile network doesn't work in the same way as the wifi.
One example on how to find the url, in this screenshot the url is https://school.moodledemo.net:
