Do I have to pay an Impark ticket?

I got a ticket last night for parking in an Impark lot. I saw "event pricing" on the way into the lot and assumed it was pay upon exit. Wrong! There was a QR code (which I initially missed) and I was supposed to pay using that or at the machine before leaving my car. I tried calling them and they said there's nothing they can do -- it's $81. Which seems steep for an innocent mistake. I have never gotten a ticket before, so I'm not sure what happens if I don't pay it.