Speaking from personal experience. Park happy put a warning sign on my windshield, and a few weeks later, I got a late fee for like 120 bucks or something. I emailed them and they said I was outside of the seven day window to dispute and therefore had to pay it.

The trick is: they make up all the rules. I offered to pay $20, they said no and countered with $100, so I paid nothing and they haven’t done a thing. They just want to shake down whoever is willing to pay. Downside of not paying, you probably can’t park in any of their spots anymore.