Applying a Customer Deposit to a Final Invoice

SUGGESTED

Hi there. So, I work for a construction company, and a lot of time we have drawdowns to what a person will owe on their contract amount. The issue that I have always come to their final billing. The client always makes a 10% deposit of their contract price to be applied at the end when I bill them their final invoice. I can't seem to find some clear cut instruction for applying their deposit that could be made months earlier to their final invoice. I'm not sure why. Before starting here, I had about 1 1/2 weeks of Sage 50 Premium training. It would be nice to not have to contact Sage support every month if I can get instructions that seem to work and that I can rely on so any advice is most welcomed.