Typically you invoice for a deposit using a service type item, and that posts to a liability account (refundable deposit)
then you invoice for the total, and as the last line you use the deposit item, set the qty to negative one, and enter the deposit amount in the rate block
This is not the answer I am looking for. I need my front end entry to always be 35 % of whatever the total invoice is. Not asking how to show the negative in system asking how to make that transaction set to self math itself. If that makes any sense. I know how to take a frontend deposit and put it in the invoice.