I have a client that we have been billing now for about 1.5 years and they are holding 10% back from invoicing. The way the billing has been done by a previous book keeper was just doing it as a receivable and leaving the amount to go over 91+ days. My question is how do I properly do the invoice showing the 10% hold back and keep track of each lot the customer has from this point on? 

Thank You 

Amanda T