If you use the SudTirolMobil app to plan a journey, it gives the option of buying a ticket/s. But it says the ticket must be validated when boarding a bus. I'm in S Tirol now and been on a bus (had a free bus pass from the hotel) and validating involves inserting a physical ticket into a machine, I see nothing that is capable of scanning a QR code from an app.
So how can you validate an eTicket purched from the app?
It seems you can do it by "activating" the journey picked on the app:
https://www.suedtirolmobil.info/en/tickets/fare-system-and-ticket-validation/smartphone-check-in