UBL-SR-02:CAC/CBC namespace declarations required
Fix: Add cac and cbc namespace declarations.
UBL requires Common Aggregate and Basic Component namespaces.
Engine Classification
Requires user confirmation before application
What is UBL-SR-02?
UBL-SR-02 is a fatal validation rule defined in the ubl-2.1 specification. It validates the ReceiptDocumentReference 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:ReceiptDocumentReference
Why This Error Matters
Invoice will be rejected by EN16931 validators. These structural constraints ensure consistent processing by receiving systems.
UBL-SR-02 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-02
- ·Specification: ubl-2.1
How to Fix It
Add cac namespace
xmlns:cac="urn:oasis:names:specification:ubl:schema:xsd:CommonAggregateComponents-2"
Add cbc namespace
xmlns:cbc="urn:oasis:names:specification:ubl:schema:xsd:CommonBasicComponents-2"
XML Example
Generic example based on the rule's target XPath. Your actual XML structure may differ.
<!-- Required block is missing --> <!-- <cac:ReceiptDocumentReference> ... </cac:ReceiptDocumentReference> -->
<!-- Add the required block --> <cac:ReceiptDocumentReference> <!-- child elements --> </cac:ReceiptDocumentReference>
Technical Reference
/Invoice/cac:ReceiptDocumentReferenceCommon 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-02 automatically. See the fix response →
Frequently Asked Questions
UBL requires Common Aggregate and Basic Component namespaces.
Add cac and cbc namespace declarations. Invoice Navigator can propose a fix for this error, which you review and confirm before it is applied.
Yes, UBL-SR-02 is a critical error that will cause invoice rejection. It must be fixed before submission.
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Last updated: 3 March 2026
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