# BR-21

> Each Invoice line (BG-25) shall have an Invoice line identifier (BT-126).

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/br-21

## Official rule text

Each Invoice line (BG-25) shall have an Invoice line identifier (BT-126).

## Why did my invoice fail BR-21?

Each Invoice line (BG-25) must have an Invoice line identifier (BT-126) that is unique within the invoice. This identifier lets buyers, sellers and systems reference a specific line unambiguously (for matching, disputes and remittance). The rule ensures every line is individually addressable.

## Common causes

- A cac:InvoiceLine is missing its cbc:ID element.
- Line IDs were duplicated across lines, so at least one line effectively lacks a distinct identifier.
- The ID element was emitted empty because the source line number was null.

## How do I fix it?

```
<cac:InvoiceLine>
  <cbc:ID>1</cbc:ID>
  <!-- ... -->
</cac:InvoiceLine>
```