Not able to do Vendor Returns on DropShip PO

1) Created an RMA Order to bring back the unit to Drop Ship Org were the PO is created.

2) Received RMA order to the Drop Ship Org.

3) RMA got Invoiced and credited the Original Sales Order.

4) Navigate to Purchasing Responsibilities> Returns and query for the PO number which was Invoiced and matched.

5) Getting APP-PO-14094 Error message and not able to do Return to Supplier to get credit from the Supplier.

6) PO is Approved and not cancelled. Qty billed and qty received match on the PO line.

Why I am not able to do Returns on the PO which is Invoiced