Message SAP BORGR558 - The inbound delivery still has items that do not refer to a PO

Diagnosis Delivery type &v1& does not allow you to save an inbound delivery whenone or more items do not have a reference to a purchase order. System Response The system cannot save the inbound delivery. Procedure Either complete the items that do not refer to a purchase order use a different delivery type that allows incomplete inbound deliveries change delivery type &v1& accordingly