To apply a prepayment or other payment documents to this invoice received, click 
(the Edit prepayment offset button) to the right of the Prepayment field at the bottom of the form. This opens the Offset Prepayment dialog box to be used for selecting payments made earlier to the supplier.
The "Invoice Received (create)" form. The Offset Prepayments dialog box
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To automatically apply the payments to the invoice received, click the Auto Fill button. The system selects the documents starting from the earliest ones (by using the first-in first-out rule) until either all the available documents are applied or the amount of the applied documents becomes equal to the invoice amount.
To manually apply a prepayment, select a prepayment in the upper pane and double-click it. Repeat for other prepayments if needed. Use the Up and Down arrows in the group 
of arrows to rearrange the documents in the lower pane. Then, in the Amount column, you can edit the amounts of the payments that must be applied—the remaining amounts in the upper pane will be adjusted accordingly.
| Note. If any prepayment has been applied to the invoice received, on invoice received posting, the total VAT amount is recalculated as VAT for the remaining open amount. (Open amount is the document amount minus the sum of prepayment amounts). |
You can view all the involved amounts and VAT amounts on the print form of the tax invoice received. |
The Total Accounts Amount field shows the total applied amount in the currency of the invoice received.
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