Watch out for being tricked by Kingparking.
I have parked at Kingparking Fiumicino numerous times.
On one of the occasions when I picked up my car they claimed I had not paid in advance. Not having the receipt with me I had to pay again, obviously expecting we could sort it out later.
However, despite me sending written proof of the double payment and originally promissing to pay back the double payment, and despite numerous emails with reminders, Kingparking is now completely ignoring my claim and is keeping the double payment, despite knowing they have no right.