I can't agree with this. The time to find your wallet is the same as to find your phone and then after that it's: grab cash vs. unlock phone + wait for phone to load + find app + wait for app to load + find ticket in app... not to mention hope your internet is good + hope your phone hasn't died + hope you haven't been logged out of the app for some reason, etc... and a lot of that happens even if you do have your phone ready and it just enters the lock screen on you while you're pulling up to the parking attendant. I think you'll have more people that won't have the right screen on their phone ready to go and there's a lot more going on that can make it take longer than simply paying with cash or showing some sort of printed ticket. Screenshot the QR code or bar code or whatever it is. Then all you have to do is open your photos, click the photo with the code and get it scanned. Simple, takes two seconds.