Interproject Billing with Sponsored Receiver Project

Hello,
I have been trying to test interproject billing and was able to get it to work between non-sponsored provider and receiver projects. Provider and receiver projects are in two different business units under the same legal entity. Next, I have been trying to test the functionality with non-sponsored provider project and sponsored receiver project in two different business units but same legal entity. When I go to import the AP invoice, Invoice is not being generated and the Output report is giving me a message that contract, and funding source are missing. Not sure what setup am I missing. I