UBL-SR-01:UBL namespace declaration required
Fix: Add correct UBL 2.1 namespace declaration.
UBL documents must declare correct namespace.
Engine Classification
Requires user confirmation before application
What is UBL-SR-01?
UBL-SR-01 is a fatal validation rule defined in the ubl-2.1 specification. It validates the ContractDocumentReference element in the UBL invoice XML.
When this rule fires, the invoice is rejected by Peppol access points and never reaches the buyer.
Target path: /Invoice/cac:ContractDocumentReference
Why This Error Matters
Invoice will be rejected by EN16931 validators. These structural constraints ensure consistent processing by receiving systems.
UBL-SR-01 is a hard failure — the invoice must be corrected and re-sent before it can reach the recipient.
Validator Behavior
- ·Causes invoice rejection
- ·Fails UBL schema validation
- ·Error returned: UBL-SR-01
- ·Specification: ubl-2.1
How to Fix It
Check namespace
xmlns="urn:oasis:names:specification:ubl:schema:xsd:Invoice-2"
Add if missing
Include on root element
XML Example
Generic example based on the rule's target XPath. Your actual XML structure may differ.
<!-- Required block is missing --> <!-- <cac:ContractDocumentReference> ... </cac:ContractDocumentReference> -->
<!-- Add the required block --> <cac:ContractDocumentReference> <!-- child elements --> </cac:ContractDocumentReference>
Technical Reference
/Invoice/cac:ContractDocumentReferenceCommon 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
Seeing this in production? The API handles UBL-SR-01 automatically. See the fix response →
Frequently Asked Questions
UBL documents must declare correct namespace.
Add correct UBL 2.1 namespace declaration. Invoice Navigator can propose a fix for this error, which you review and confirm before it is applied.
Yes, UBL-SR-01 is a critical error that will cause invoice rejection. It must be fixed before submission.
Related Errors
Related Content
Last updated: 3 March 2026
Validate your invoice
Drop your XML here to check for UBL-SR-01
Fix UBL-SR-01 with one click
Upload your invoice and we'll suggest a fix for your review before applying it.