When part of a customer's invoice has been left unpaid and the customer has left
If the customer has left the school or doesn't intend to pay the remainder of the invoice, there is a method to deal with the debt using credit.
You will need to add a credit for the remainder of the amount to write off the invoice. This is not a payment and will mean that any billing records are reconciled correctly.
Firstly, go on 'Billing' > 'Add Credit':
Once on the tab, choose the customer in question and add the amount that remains on the invoice. Then, press 'Create'. The debt will disappear and the account will be balanced.
Another alternative is to edit the invoice itself so that the amount stated in it and the amount paid match. See how to edit a part-paid invoice here.
In the end, if the customer has left you can just delete them or make them inactive!