If seller is icelandic and invoice contains supporting description EINDAGI the id date must be same or later than due date — Ef seljandi er íslenskur þá skal eindagi (BT-122, DocumentDescription = EINDAGI) skal vera sami eða síðar en gjalddagi (BT-9) ef eindagi er til staðar.
Explanation
The EINDAGI date must be on or after the due date.