PEPPOL-EN16931-F001
An official OpenPeppol BIS Billing 3.0 rule – checked for invoices sent over the Peppol network on top of the EN 16931 rules.
What this error means
PEPPOL-EN16931-F001
A date in the document is not in YYYY-MM-DD format.
How to fix it
Write all dates as YYYY-MM-DD, e.g. 2026-07-08 — no time part, no other separators.