Writing off outstanding balance

Wondering how to write off a customers balance.

A customer owes $100, however I want to write this total off as a gesture of goodwill without deleting said invoices.

Is there a way to do this so that the customers account shows as $0 without increasing my “money received” columns?

The right thing would be to issue credit note under Credit notes tab for $100 and then transfer the credit from credit note to unpaid sales invoice so there will be nothing owing on the invoice.

See: Use credit notes for customer returns and refunds | Manager

Also, there is Wikipedia article on use and purpose of credit notes.