Since yesterday April 24th, 2024, you can pay for the bus to and from the airport by simply passing your credit card or your smartphone / smartwatch on the ticket machine in the bus. The price of the journey remains the same as with a paper ticket.
There is no need for any app.
It is currently only valid on buses to and from the airport (X93, X95, X96, X97) and will soon be available on all buses.