BR-2: invoice number missing
The invoice does not contain an invoice number (BT-1). This is one of the fundamental mandatory fields of EN 16931 — without it the file is rejected by every compliant validator, including Chorus Pro and Peppol access points.
Last updated: 2026-07-07
Affected field
BT-1 Invoice number / cbc:ID (UBL) / rsm:ExchangedDocument/ram:ID (CII)
Cause
The invoice number field was left empty at export, or the invoicing software's field mapping points at a blank source field. Some tools emit the XML element but leave it empty, which triggers the same error.
Fix
Populate a unique invoice number in cbc:ID (UBL) or rsm:ExchangedDocument/ram:ID (CII). The value must be non-empty; EN 16931 imposes no specific format, but it must uniquely identify the invoice within your sequence.
<ubl:Invoice> <!-- ERROR: empty element --> <cbc:ID></cbc:ID> </ubl:Invoice>
<ubl:Invoice> <cbc:ID>INV-2026-0042</cbc:ID> </ubl:Invoice>
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Frequently asked questions
My software does export a number — why the error?▼
Check that the XML element is not empty or whitespace-only. The error also fires when the number ends up in a different element (such as an order reference) instead of BT-1.
Is there a required format for the invoice number?▼
No. EN 16931 only requires that an identifier (BT-1) is present. Sequencing and chronology requirements come from national tax law, not from the technical standard.