Have your System Administrator complete the following.
Go to Setup > Property Options > General Information in RMS.
Navigate to the 'Reservations' tab.
Select the checkbox 'Show Reg No's'.
Select 'Save/Exit' to store the changes made.
Log out of RMS to allow the database to update with the changes made.
This will display allow for Boomgate Access Numbers to be created on a Reservation for a specific Car Registration Number.