Buy To Order? How to receive partial PO for SO - without issues?

Am using BUY TO ORDER (set on part master) as the FG’s are made to order for a specific customer and cannot be shipped to another customer. When a PO is issued to a supplier, and they only ship a partial - what is the best way to handle this once asked if wish “to close this release”? Obviously we want the PO to be received complete - what is the best practice for receiving a partial PO linked to a Buy To Order SO?