errorubl-2.1

UBL-SR-01:UBL namespace declaration required

UBL documents must declare correct namespace.

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AUTO-FIX

Auto-fix: Keep the first occurrence and remove duplicate elements. EN16931 requires exactly one of this element.

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Why This Error Matters

Invoice will be rejected by EN16931 validators. These structural constraints ensure consistent processing by receiving systems.

How to Fix It

1

Check namespace

xmlns="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2"

2

Add if missing

Include on root element

Technical Details

XPath: /Invoice/@xmlns

Common Causes

  • ERP system exports multiple references where only one is allowed in EN16931
  • Data consolidation merged records that should have been deduplicated
  • Template or mapping incorrectly configured to output duplicate elements
  • Manual editing introduced extra elements
  • Invoice conversion from another format did not merge duplicate entries

Frequently Asked Questions

UBL documents must declare correct namespace.
Add correct UBL 2.1 namespace declaration. You can also use Invoice Navigator's automatic Fixer tool to correct this instantly.
Yes, UBL-SR-01 is a critical error that will cause invoice rejection. It must be fixed before submission.

Related Errors

UBL-SR-02

CAC/CBC namespace declarations required

Last updated: 16 January 2026

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