If seller is icelandic and invoice contains supporting description EINDAGI invoice must have due date — Ef seljandi er íslenskur þá skal reikningur sem inniheldur eindaga (BT-122, DocumentDescription = EINDAGI) einnig hafa gjalddaga (BT-9).
ubl-creditnote:CreditNote[$SupplierCountry = 'IS'] | ubl-invoice:Invoice[$SupplierCountry = 'IS'](exists(cac:AdditionalDocumentReference[cbc:DocumentDescription = 'EINDAGI']) and exists(cbc:DueDate)) or not(exists(cac:AdditionalDocumentReference[cbc:DocumentDescription = 'EINDAGI']))