how ca I Receipt RI - PO with prepayment

 Hi all,I have the following scenario...

We're in Brazil and here we have Integrated Receiving (RI), which is a module specific to calculate Brazilian taxes. So, we do receiving through RI.

Now, there are some "Purchase Orders" with an advance payment, were associated on a "prepayment" from Payables Invoice Workbench.

The detail is when you want to create the receipt from RI, because you can not find the PO of the prepayment.

How can I view the PO's and create the receipt for the standard invoice?

Thanks in advance,

Isabel Molina