Parking at the plaza can be very difficult since the parking spots are very tight, so I would recommend bringing a small car (SUV, not a truck) or park at Walmart/Ala Moana Mall if you're getting food for an hour or have an appointment that wouldn't take too long.
Parking is $1 per 30 minutes and usually get validation stamp until 5:30pm since the parking attendant leaves around that time, but I recommend paying online with the QR code if you plan to stay longer than 3 hours such as being at cafe Gangnam, which is a karaoke/bar place. However, there is a $1.10 fee unfortunately and it is $2 an hour is reasonable and you can add more hours to pay, but the website isn't perfect either since it gave me different times to pay for my car (6:56pm-9:56pm) when I wanted to pay for 6-10pm. read more