What it means
The project reference (BT-11) is the identifier of the project the invoice relates to. It may appear only once on the invoice or credit note, in cac:ProjectReference/cbc:ID directly under the document.
Why it matters
EN 16931 allows at most one project reference per invoice or credit note.
How to fix it
Check the project field in your invoicing software and keep a single value. In the XML there must be at most one cac:ProjectReference/cbc:ID directly under the invoice or credit note.
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
Project reference shall occur maximum once. 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-SR-39 still fails, and which other rules do.
Related rules
- UBL-SR-40 The buyer can have only one trade name
- UBL-SR-42 A seller can have at most two tax scheme entries
- UBL-SR-43 Only the invoiced object reference may carry a scheme identifier
- UBL-SR-44 An invoice can have only one payment reference
- UBL-SR-45 Only one due date in the payment means
- UBL-SR-46 The payment means text can only be given once