If you are trying to enter a vendor invoice with multiple POs on the invoice, do the following:
1) Go to P0411, enter the supplier number and all other header information EXCEPT the PO number
2) From Row exit, select "Receipts to Match"
3) Enter the first PO number on the vendor's invoice and click find. Select the lines you want from this PO and click ok to bring selections back to the initial screen
4) Repeat step 2)
5) Enter the next PO number on the vendor's invoice and click find. Select the lines you want from this PO and then click "OK" to bring the selections back to the initial screen.
6) Repeat process as necessary to bring in all the received lines from the various POs.
7) Make any adjustments to bring remaining amount to zero. Click ok to save voucher