You can manually overlock the unit and restrict customer access. Here's how:
Select the customer subscription and then select the 3 dots option, as below. Select the Overlock option, which ensures the customer cannot access the unit.
Returning access
Should you wish to grant access back to the customer, you can change the status to Remove Overlock by following the same steps above.
Note: You can also turn on auto-lock if you're using a Smart Entry system and wish for a unit to be automatically locked if a customer's payment fails. Learn more about auto-overlocking here.