PO - What is the best way to write off and close remaining amount on Amount Only PO?

For a PO with amount only.

For example. An amount only PO was created with $2500.   Then a receipt is entered with $2500.
The invoice amount is $2000 and this amount is paid.

The $500 is left in the receipt and PO, what is the best way to write off this remaining amount in receipt and PO?

NOTE - The customer doesn't use commitment control.

Thanks,