I have been parking at preflight for years. Well before they built the parking structure. The structure is a bit of hassle as you have to scan your card at checkpoints as drive up to the roof Parking.
I called from the curb as it was late and waited and watched as Parking bus after Parking bus passed me by. I finally saw the preflight bus and was picked up. It was probably 15 minutes.
So it was late at night from a New York trip. I had printed out a voucher for one free night from my awards points with preflight. As I exited the lot I gave the voucher to the employee who proceeds to tell me there's no bar card on my voucher and she can't honor the free day of Parking.
She suggested I could go into the office and discuss with the manager on duty. However, after a 6 hour flight it was late almost midnight and I didn't feel like getting out of my card and talking with the manager.
Overall not a very good experience.