The total amount of the payment, in the payment currency. It must reconcile against whichever list is set. The five document-linked lists (invoice_payments, bill_payments, credit_note_payments, debit_note_payments, payslip_payments) are summed by amount_to_pcy; the two advance blocks (credit_notes, debit_notes) carry no amount_to_pcy and are summed by amount instead. For money-out payments (bill_payments, credit_note_payments, payslip_payments, debit_notes) amount equals that sum plus payment_fees; for money-in payments (invoice_payments, debit_note_payments, credit_notes) it equals that sum minus payment_fees. Must be greater than zero.