What it means
Every invoice must contain the invoice number (BT-1). It is the number that identifies this invoice uniquely in your records.
Why it matters
EN 16931, the European e-invoicing standard, makes this field mandatory. Without it the recipient's system rejects the invoice before anyone reads it, and public bodies and Peppol access points refuse it outright.
How to fix it
Give the invoice a unique number from your own numbering sequence, such as 2026-0042. Most invoicing software assigns it when you finalise the invoice, so make sure you export the final invoice and not a draft.
The rule as published
An Invoice shall have an Invoice number (BT-1). Business terms: BT-1
Where this rule applies
| Rule set | Version |
|---|---|
| EN 16931 (UBL) | 1.3.17 |
| EN 16931 (UBL credit note) | 1.3.17 |
| EN 16931 (CII) | 1.3.17 |
| XRechnung 3.0 (UBL) | 3.0.2 |
| XRechnung 3.0 (UBL credit note) | 3.0.2 |
| XRechnung 3.0 (CII) | 3.0.2 |
| Peppol BIS Billing 3.0 (invoice) | 2026.5 |
| Peppol BIS Billing 3.0 (credit note) | 2026.5 |
| Factur-X 1.09 MINIMUM | 1.0.9-2 |
| Factur-X 1.09 BASIC WL | 1.0.9-2 |
| Factur-X 1.09 BASIC | 1.0.9-2 |
| Factur-X 1.09 EN 16931 | 1.0.9-2 |
| Factur-X 1.09 EXTENDED | 1.0.9-2 |
| ZUGFeRD 2.5 MINIMUM | 2.5.2 |
| ZUGFeRD 2.5 BASIC WL | 2.5.2 |
| ZUGFeRD 2.5 BASIC | 2.5.2 |
| ZUGFeRD 2.5 EN 16931 | 2.5.2 |
| ZUGFeRD 2.5 EXTENDED | 2.5.2 |
| SI-UBL 2.0 / NLCIUS (invoice) | 2.0.3.13 |
| SI-UBL 2.0 / NLCIUS (credit note) | 2.0.3.13 |
| NLCIUS (CII) | 1.0.3.13 |
| France CTC (UBL invoice) | 1.4.0-04 |
| France CTC (UBL credit note) | 1.4.0-04 |
| France CTC (CII) | 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 BR-02 still fails, and which other rules do.