This Tutorial will explain the process of closing an account.
This will be relevant if the account is not going to be invoiced for whatever reason (freebie bookings, etc.).
Open the NightsBridge calendar
Click on "View Invoice/Payment details for this booking"
Click on the button with the calculator icon to open the account which the booking is linked to.
Click on Close Account (A/C)
Remember that you should only do this if you are not going to invoice the client.
You will be prompted to confirm that you're not going to generate an invoice on this account.