If you have obtained an advance payment for an invoice being entered using an advance invoice, you can connect the advance invoice to the final invoice. As a result, the amount paid in advance will be deducted from the final invoice. The printed invoice will include references to the connected advance invoices if the Print Advance Payments information on Customer Invoice option is enabled in the Company/Invoice tab.
An advance invoice which is paid or partly paid should exist.
The advance invoice will be connected to the final invoice and the final invoice information will be adjusted accordingly. (postings, due amount etc.,). Until the final invoice is paid in full, the status of the invoice would be Partly Paid.