User wants to associate an expense entry to an existing invoice in BillQuick.
This is called progress billing in BillQuick. You can link your expense entries (or time entries) to existing invoices in BillQuick by following these steps:
1. Open the Expense Log screen and select the View By Project mode.
2. Click Tools > Change and select the relevant Invoice # from the drop-down.
3. Click OK. Your expenses and invoice is linked now!
Note: You also have the option to recalculate the markup. What that means is if you want to adjust the value of the entries to match (make equal) the amount that was previously invoiced.