BR-21:Missing invoice line identifier
Each Invoice line shall have an Invoice line identifier (BT-126). This is a unique sequential number identifying each line item on the invoice.
Engine Classification
Auto-fix: Generate sequential line identifiers (1, 2, 3...) for each invoice line. These are internal reference numbers, not product codes, so sequential generation is safe.
What is BR-21?
BR-21 is a fatal validation rule defined in the EN 16931 specification. It validates the ID 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: cac:InvoiceLine/cbc:ID
Why This Error Matters
Invoice rejected. Line identifiers are required for referencing specific items in disputes or corrections.
BR-21 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.
Invoice Navigator can automatically correct this error in your pipeline. The fix is applied with full audit evidence, so your compliance trail remains intact.
Validator Behavior
- ·Causes invoice rejection
- ·Error returned: BR-21
- ·Specification: EN 16931
How to Fix It
Identify lines without ID
Find all cac:InvoiceLine elements that are missing the cbc:ID child element
Add sequential IDs
Insert <cbc:ID>1</cbc:ID>, <cbc:ID>2</cbc:ID>, etc. as the first child of each InvoiceLine
Verify uniqueness
Each line ID must be unique within the invoice (1, 2, 3... is the common pattern)
Before / After
<cac:InvoiceLine> <!-- cbc:ID is missing --> </cac:InvoiceLine>
<cac:InvoiceLine> <cbc:ID>valid-value</cbc:ID> </cac:InvoiceLine>
Technical Reference
cac:InvoiceLine/cbc:IDCode Example
<cac:TaxCategory>
<cbc:ID>S</cbc:ID>
<cbc:Percent>21</cbc:Percent>
<cac:TaxScheme>
<cbc:ID>VAT</cbc:ID>
</cac:TaxScheme>
</cac:TaxCategory>Common Causes
- ·Invoice line ID field not mapped in export template
- ·Source system uses row ordering not explicit IDs
- ·Export template missing InvoiceLine/ID field
- ·Line identifiers not generated by source system
- ·ID field present but contains empty or null value
Seeing this in production? The API handles BR-21 automatically. See the fix response →
Commonly Seen In
Frequently Asked Questions
VAT category S (standard rate) must include the applicable percentage.
Add the VAT percentage for standard rate items. You can also use Invoice Navigator's automatic Fixer tool to correct this instantly.
Yes, BR-21 is a critical error that will cause invoice rejection. It must be fixed before submission to ensure your invoice is accepted by the recipient's system.
Many instances of BR-21 can be automatically corrected using Invoice Navigator's Fixer tool. Upload your invoice and the tool will identify and fix common issues, including standard rate category must have percent.
BR-21 is commonly seen in exports from All invoicing software. These software packages sometimes generate invoices that need adjustment to meet full compliance standards.
See Also
Related Errors
Last updated: 27 February 2026
Handle BR-21 Automatically in Your Pipeline
The compliance engine auto-remediates this error with controlled safety policies and evidence pack generation.