I've seen a city that uses Passport Parking refund the unused time. They also use PayByPhone with the same location code, and using that method did not refund the unused time.

This is how parking works with applications in Finland and I want to assume everywhere else in Europe. This is the main reason a lot of people switched to apps if I had to guess (I almost never see people use the coin operated machines on the parking lots used anymore except by tourists)

Yeah, if I remember correctly the initial business model of paybyphone was precisely that they were pocketing the overlap between parking sessions and using that to deploy at no cost for the city and invisible cost for the drivers