The app shows some generic error about not being able to properly get precise location and links to a generic help page (https://support.fairtiq.com/hc/en-us/articles/360001395880--Solving-location-issues). I have of course followed all tips on that site. This happens also after allowing the appprecise location, unrestricted battery etc.
The point is that the app has to constantly track your location because it bills public transport rides by distance, so they have to make sure that you do not quickly go a bit further and then back again.
I tried disabling the GrapheneOS-specific hardening and ala tried with a new user with Play Services, to no avail. (I would prefer using ist without Play Services, though.)