The estimate ID
OK
What is still collectable on this bill. Always 0 for a terminal invoice (Void, or Superseded by a payment-time merge): the write paths refuse those, so reporting a non-zero figure advertises a payment that can only fail (ITE-326). The obligation on a merged source lives on its successor — see bool InvoicePaymentSummaryDto.IsPayable.
False when the invoice's status refuses payment (Void / Superseded). Lets a client distinguish "nothing left to collect because it's paid" from "this bill can't take money at all" — both of which read as balanceDue == 0.