What it means
When an invoice or credit note refers to an earlier invoice, EN 16931 carries only that invoice's number (BT-25) and date (BT-26), in cac:BillingReference/cac:InvoiceDocumentReference. This rule checks that the reference does not also contain cac:Attachment, a block that holds an embedded file or a link to one.
Why it matters
The EN 16931 UBL rules do not use attachments inside the reference to an earlier invoice. Additional supporting documents have their own document-level group (BG-24).
How to fix it
Remove cac:Attachment from cac:BillingReference/cac:InvoiceDocumentReference, keeping the earlier invoice number (BT-25) and any existing invoice date (BT-26). If you still need the attachment, include it in a document-level cac:AdditionalDocumentReference as an additional supporting document (BG-24). Check the corrected file again.
Once the file is corrected, check it again for free: Validate an invoice against EN 16931
Or fix the invoice in a form and download the corrected file, for 1 credit: Fix a rejected e-invoice
The rule as published
A UBL invoice should not include the BillingReference Attachment Where this rule applies
| Rule set | Version |
|---|---|
| EN 16931 (UBL) | 1.3.17 |
| EN 16931 (UBL credit note) | 1.3.17 |
| XRechnung 3.0 (UBL) | 3.0.2 |
| XRechnung 3.0 (UBL credit note) | 3.0.2 |
| Peppol BIS Billing 3.0 (invoice) | 2026.5 |
| Peppol BIS Billing 3.0 (credit note) | 2026.5 |
| SI-UBL 2.0 / NLCIUS (invoice) | 2.0.3.13 |
| SI-UBL 2.0 / NLCIUS (credit note) | 2.0.3.13 |
| France CTC (UBL invoice) | 1.4.0-04 |
| France CTC (UBL credit note) | 1.4.0-04 |
| CIUS-RO UBL Invoice 1.0.9 | 1.0.9 |
| CIUS-RO UBL Credit Note 1.0.9 | 1.0.9 |
Check your file
Drop your e-invoice to see whether UBL-CR-034 still fails, and which other rules do.
Related rules
- UBL-CR-035 Do not send a validity period in the earlier invoice reference
- UBL-CR-036 Do not send an issuer party in the earlier invoice reference
- UBL-CR-037 Do not send a verification result in the earlier invoice reference
- UBL-CR-038 Do not use the self-billed invoice reference
- UBL-CR-039 Do not use the credit note document reference
- UBL-CR-040 Do not use the self-billed credit note reference