BR-01 error
What this rule checks
Explanation
Every e-invoice must declare which technical specification it follows — this is the "Specification identifier" (BT-24), a fixed identifier string that tells validators (and the recipient's software) it's an EN 16931-compliant invoice, not just a general-purpose UBL or CII document.
How to fix it
Add the CustomizationID (UBL) or GuidelineSpecifiedDocumentContextParameter/ID (CII) element with the standard EN 16931 specification URN, e.g. urn:cen.eu:en16931:2017. Most invoicing software sets this automatically once you select an EN 16931/Factur-X profile — check your template or export settings.
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