If you go to make a reservation and the system is saying you have already maxed out your reservations please check the rules that are listed on the reservation page. Some locations will have rules such as a maximum amount of reservations per account and/or license plate.
This will prevent you from making a new reservation until one of them expires or is cancelled.
Guests run into issues when they are trying to make a reservation for a rental vehicle and they try to use 'TBD' or 'RENTAL'. Placeholders like that are used up immediately and therefore we advise to use your home vehicle or a random word as a placeholder to make a reservation. You can always adjust the plate when you get the rental vehicle.
The rules are always listed in the FAQ of the Parking Website and on the reservation website as well.