I sent them the following question:
It appears from the screenshot on Google Play, that some garages will require a pass to be displayed in the windshield for the the duration of the time parked. If I book from the mobile app, how will I have something to leave in the windshield?
This was their reply:
Hi AnonymousUser,
Unfortunately not all locations accept mobile passes. When browsing on our app, locations that do not accept mobile passes are grayed out, and also contain prominent red disclaimers indicating you need a printed pass for validation.
We also offer locations that only need your license plate info for validation that we list as mobile pass-friendly. So while you technically don’t show a mobile pass for validation, you also do not need a printed-out pass, as the attendants just check your license plate to verify your parking. Hopefully that clears this up, but if you have any other questions, let me know.