This idea has been merged into another idea. To comment or vote on this idea, please visit S1-I-109 Add 'Date Paid' to Sales Invoices & Purchase Invoices Summary Page.
When a Sales Invoice is part or fully paid, the onscreen display shows a flag to confirm this. If invoice is then printed, it is not immediately obvious that it has been paid - need to look around the page to read the figures.
Much better if a large dated PAID stamp is added to the page near the top in a prominent position. I can send you a sample PDF showing how it appears on my previous QuickBooks invoices.