Contractor Invoicing When Customer Only Takes Partial Receipt

For a commercial item FFP supply contract, is the contractor entitled to invoice in full if the customer only takes partial receipt?

For example, a purchase order has one CLIN for 500 units with a unit price of $750 for a total contract value of $375,000. The customer only received 300 units even though the contractor attempted to deliver all 500 units. If the vendor is only entitled to be paid for the 300 units delivered, what options does the vendor to recoup any related costs associated with attempting to deliver the remaining units? Appreciate any feedback!