How to make a Supplier site not visible when raising a requisition without affecting BU's functions?

Summary:

How to make a Supplier site not visible when raising a requisition without affecting Business unit's functions.

We are trying to make a Supplier site for BU X not visible when raising a requisition for Requisitioning BU Y. So to that, we remove the Site assignment for BU Y on the Procurement BU X site. But when we remove that site assignment, we can no longer create an invoice on the Purchase Order with Requisitioning and Procurement BU X and a Bill to BU of BU Y.

Note BU Y has shared procurement service with BU X.

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