My supplier delivered half the chicken I ordered. What do I type when I receive the purchase order?

Type what actually arrived, not what you ordered. Open Menu → Purchase orders, open the order, and under Receive the delivery put the real quantity and the cost per unit from the invoice beside each line. Press Received and put it on the shelf. The half that came lands on the shelf, the average cost moves towards what you paid, and the order closes with its real total. The missing half is not forgotten: the Reorder column on Ingredients & suppliers asks for it again the next time you open Fill to par, because the order is now closed and no longer counts as stock on its way. Short deliveries are normal, and the point of a restaurant stock management system is that the shelf tells the truth.