How can you bring in the amount a customer has paid against an open invoice?

@aaronslim, your spreadsheet shows 0.00 in Original Retainage and Unreleased Retainage on both invoices, and Total Amount equals Amount. So Acumatica has no retainage recorded on those two. Whatever the customer held back is part of the regular Balance.

That export is the Invoices and Memos list, and it has a Balance column that's hidden by default. Open the gear at the top left of the grid (Column Configuration) and check Balance. Paid to date is Amount minus Balance. It covers everything applied and released against the invoice, so an applied credit memo counts along with customer payments.

If you'd rather see paid to date as its own column than subtract in Excel, build a generic inquiry on ARInvoice and add a result column with this formula:

=[ARInvoice.CuryOrigDocAmt]-[ARInvoice.CuryDocBal]

You'll see a Total Paid field on ARInvoice too. I'd leave it out. It counts applications that haven't been released yet, so it can run ahead of what's actually been paid.

On invoices that do carry retainage, Amount excludes it, Total Amount adds it back, and Unreleased Retainage holds it until you release it. Once released, the retainage bills on its own invoice with Retainage Document checked and Orig. Ref. Nbr. pointing back to the original. Payments against it land on that invoice.