With the app, I have to do all of that once and the app remembers everything for me. If I am driving my wife's car, I don't have to try to remember her plate number. I can pay for my parking while walking to wherever I am going and I'll get a notification 5 minutes before my payment expires and can add time right where I stand at that moment. Parking apps can be great though it is annoying that every town seems to have their own app or payment provider.
Edit: just to elaborate a bit further in case it's not clear: should people who don't have a smartphone, or their smartphone is broken, or maybe they forgot the charger home, still be allowed to park their vehicle in a public area? Isn't there a higher standard in terms of accessibility requirements, when you are providing a public service?
Thankfully there are still kiosks that accept physical credit cards so I am able to legally park my car. It's a lucky thing I have a credit card that hasn't been banned because there no longer seems to be any way to pay with quarters.
In some cities the parking meters are run by a private company.
Chicago, for example, leased its parking meters to an Australian company. (Or Spanish. I forget, one got the parking meters the other got the Skyway) In exchange for an up-front payment to the city, the private company gets to run the parking meters almost any way they want.
This includes raising prices.
Or worse, in the Chicago example, the parking meter company successfully sued the city and now Chicago isn't allowed to permit the construction of any new public parking garages in the downtown core, because that would hurt the parking meter business. The only new garages that are permitted are for new residential buildings and a calculated number of spaces exclusively for office buildings for hotels.
If city's hands are tied for more car-centric infrastructure, now they can spend that budget on bike lanes, citibikes, and other transit projects.
Scammers can still put fake stickers/posters/whatever up, but the QR scanner shouldn't trigger an action, it should just provide some static location data when it comes to some payment action.
I think it's just a really poorly thought out system that didn't really research how other successful implementations of QR codes work.
It should not be an app. Or there could be an app in addition to other methods of paying.
Edit: the reason is accessibility and the fact that they are providing a public service https://news.ycombinator.com/item?id=29818536
I suppose this is harder to pull off with a lower benefit, and a higher chance of getting caught (i.e. fast acting law enforcement would know which car was in the free space).
To mitigate this, you might need space numbers posted. This is easy to verify that each space is different. But at this point, why even have a QR code?