Volumio doesn't work on a different network

Hi, so I have successfully set up Volumio on my home network according to this guide: https://peppe8o.com/install-volumio-on-raspberry-pi-to-get-a-smart-radio/amp/ however, when I tried to use it on a different network, it didn’t work. I powered it, connected to the hotspot (it didn’t ask for password though) but I can not reach the UI; I can see it in the list of devices that is shown when you first start the app, but when I click on it there is a permanent gray screen. Volumio.local and also do not work via the browser when connected to the hotspot. Where is the issue? I need to fix this quickly.
However interestingly I could see a half-loaded unusable UI (some elements were missing) for a couple of seconds when visiting volumio.local in a browser.