How do I add Late Fees onto an Invoice?

Example: My contract states that every 7 days after a balance is overdue, a 10% late fee will be charged. How can I add these late charges to the invoice so the customer will see them?

To add late fees (or any other product, service or surcharge) onto an invoice that has not yet been paid, you simply need to Recreate the Order. You will navigate into the Custom Package that you have for that order and add a new line item for the late fee and increase the package price as necessary to reflect the additional 10%.