Additional details on free bus implementation in Belgrade, Serbia (a city with 1.8 million people and no subway system, solely based on buses, trams and trolleybuses):
The public transportation company completely ditched their app, and just give all the data to Google Maps.
The passengers get a much better service, since Google bus combination and overall map is much better in Google Maps than in was in the old bus app...
So the passengers get a better service for free.
The city ditched not only the fare management and and the bus app, but also on the municipality police overtime, since the policemen were often giving protection ti fare inspectors...