Prepaid deposits for events or large purchases

[#1]

As an event venue, we often take deposits to hold a date for clients. We then apply that deposit to the final invoice amount, pre-tax. This often takes place online using square invoices.

There is no way for us to currently do this unless we load each client's deposit onto a gift card and then use that gift card at the end of the event to reduce the amount on the final invoice. Is there a way that we can apply a previous payment to the final amount pre tax?