How to link Ausweisapp2 with Smartphone app

I cannot link my *Ausweisapp2* to the app on my smartphone (app for german eIdentity service). Installed via snap : sudo snap install ausweisapp2-ce In the app, there are no available devices shown. * The docs say the devices must be in the same "Wifi", but my computer has cable only. * I have ufw enabled, but regarding firewall, the FAQ only talks about Windows and that it should work with default settings or the firewall would ask, which is not the case.