BT-122Supporting document reference
Official rule text
[IS-R-008] If seller is icelandic and invoice contains supporting description EINDAGI then the id form must be YYYY-MM-DD — Ef seljandi er íslenskur þá skal eindagi (BT-122, DocumentDescription = EINDAGI) vera á forminu YYYY-MM-DD.
Why this error occurs
This is an arithmetic consistency rule: the validator recomputes the amount from its components and compares it with the value in the file. It fails when the totals were computed with different rounding, when line amounts were changed after the totals were written, or when allowances/charges are counted twice.
How to fix it
Recalculate exactly as the formula in the rule text says, round each component to 2 decimals first and then sum (not the other way round), and write the result into the element. Make sure allowances are subtracted and charges added only once, and that prepaid and rounding amounts are included where the formula lists them.
What the validator checks
Checked element (context):
UBL
ubl-creditnote:CreditNote[$SupplierCountry = 'IS'] | ubl-invoice:Invoice[$SupplierCountry = 'IS']Test (XPath):
(exists(cac:AdditionalDocumentReference[cbc:DocumentDescription = 'EINDAGI']) and string-length(cac:AdditionalDocumentReference[cbc:DocumentDescription = 'EINDAGI']/cbc:ID) = 10 and (string(cac:AdditionalDocumentReference[cbc:DocumentDescription = 'EINDAGI']/cbc:ID) castable as xs:date)) or not(exists(cac:AdditionalDocumentReference[cbc:DocumentDescription = 'EINDAGI']))Check your invoice
Drop your XML or PDF on the validator and every failed rule is linked to its page here. Free, no account, the file is not stored.
Same check via API:
curl -F file=@invoice.xml https://einvoicechecker.com/v1/validateRelated rules
IS-R-009If seller is icelandic and invoice contains supporting description EINDAGI invoice…IS-R-010If seller is icelandic and invoice contains supporting description EINDAGI the id date…IS-R-001If seller is icelandic then invoice type should be 380 or 381 — Ef seljandi er…IS-R-002If seller is icelandic then it shall contain sellers legal id — Ef seljandi er…IS-R-003If seller is icelandic then it shall contain his address with street name and zip code…IS-R-004If seller and buyer are icelandic then the invoice shall contain the buyers icelandic…IS-R-005If seller and buyer are icelandic then the invoice shall contain the buyers address…IS-R-006If seller is icelandic and payment means code is 9 then a 12 digit account id must…
Frequently asked questions
What does IS-R-008 mean?
IS-R-008 is a peppol national rule: If seller is icelandic and invoice contains supporting description EINDAGI then the id form must be YYYY-MM-DD — Ef seljandi er íslenskur þá skal eindagi (BT-122, DocumentDescription = EINDAGI) vera á forminu YYYY-MM-DD.
Will my invoice be rejected because of IS-R-008?
Yes. IS-R-008 is flagged "fatal"; validators (KoSIT, Peppol access points, the German ZRE/OZG-RE portals, KSeF) reject the invoice until it is fixed.
Which formats does IS-R-008 apply to?
Only when the seller (or for some rules the buyer) is in the named country: the rule is triggered by the country code of the party. Dutch rules implement NLCIUS, German rules the XRechnung requirements inside Peppol. Syntax: UBL.
Source: Peppol BIS Billing 3.0.20 national rules (November 2025). Catalogue generated from the official rule sets on 2026-10-15.