You can manually overlock the unit and restrict customer access. Here's how:
Select the customer subscription and then select the three dots option, as shown below.
Select the Overlock option to ensure that 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.
Keep in mind that you may want to restore access only after the customer resolves any outstanding payment issues.
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.