When you receive a supplier invoice related to a purchase order, it is matched against the PO in the PO Invoices screen, here on the Purchasing menu.
Click the New button. Select the Supplier from the lookup. Enter the Invoice Number. In the PO Filter field, select the PO associated with the invoice. Select the Invoice Date.
Enter the Net Amt prior to tax and shipping. Enter the Tax Amt, if applicable. If there are shipping charges, click the Add button. Enter the Shipping Charge. Click OK.
Against each line, compare the Supplier Price with the price on the supplier invoice. If it is the same, click the Match checkbox. If the invoice price differs from the PO price, change the Supp Price, as shown here. Click Yes to update the Last Cost.
After all the lines are matched, the totals in the header should be equal to the matched amounts at right. Click Update to save the invoice. When all the lines in a PO are fully matched, the PO is automatically closed.
In summary, the key objectives of PO invoicing are to match supplier prices to verify supplier prices and to close POs after they are fully matched.