UBL-SR-02:CAC/CBC namespace declarations required
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 non-compliant and will be rejected by Peppol access points and national validation services. The sending system receives a rejection response and the invoice does not reach 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. Invoices that trigger this rule are rejected at the access point and never reach the recipient. In Peppol networks, this means your sending system receives an MLR (Message Level Response) with a rejection status. The invoice must be corrected and re-sent, adding delay to your payment cycle.
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. You can also use Invoice Navigator's automatic Fixer tool to correct this instantly.
Yes, UBL-SR-02 is a critical error that will cause invoice rejection. It must be fixed before submission.
Related Errors
Last updated: 21 February 2026
Handle UBL-SR-02 Automatically in Your Pipeline
The compliance engine auto-remediates this error with controlled safety policies and evidence pack generation.