Invoice Amount Field - Read only. The grand total of the Total Cost field in the table.
Unapplied Payments Available Field - Read only. The sum of payments that are available to be applied to this record. See Payments for information about applying payments.
Payments Applied Field - Read only. The sum of payments that have been applied to this record. See Payments for information about applying payments.
Open Balance Field - Read only. Invoice Amount minus Payments Applied.