Webapp goes offline immediately

I can’t connect to my built test webapp from my phone (or any other browser). As soon I get a connection I get “the app is offline”.

I’ve tried:
-disabling windows firewall
-port forwarding port 80 and 8080 to this pc’s ip in the router config page…

Connecting within the local wifi network (192.168.1…) works

What else should I look for ?