There are two options for adding a late fee to a debtor or a job:
1.Add a Debtors Adjustment up to the required GL account using tax code G. Then, send a statement which will show it as owing. You cannot produce an invoice from a debtors adjustment.
2.Create a non depleting stock code pointing to the required Stock GL Group. Add a job and use that stock code, then invoice the customer, then send them a copy of the invoice and a statement.
Further Information