If NIRP is possible, why not this?
Spokane Transit has an online ordering system that was crude and defective for a long time. They improved it recently, but didn't quite fix everything.
The up-down clicker on quantity is badly sized and hard to click. I accidentally clicked backwards....
What happens when you try to buy negative four passes? Fortunately for STA and unfortunately for would-be jackpot seekers, nothing happens. They didn't bother to code a limit on the clicker but they did code the 'cart' properly. The 'cart' still holds zero, not negative.