Forum Post: How to apply multiple checks to one AR invoice in same deposit?

I'm a new user of Sage 100 ERP 2013 (v 5.00.8.0) and am trying to post cash receipts.  I have a client using three checks to pay one invoice.  I entered the first check fine, but when I try to enter the second check and apply it to the same invoice it says the invoice number has already been used, would I like to accept.  After I say ok, it asks if it is a prepayment.  When I say no, it is not a prepayment, it deletes the invoice number.  How do I apply multiple checks to one invoice in the same deposit?