How to fix BR-21

What this rule checks

Every line item in the invoice must have a unique line identifier (BT-126, mapped to cbc:ID within cac:InvoiceLine). This identifier allows buyers and sellers to reference specific line items in disputes, partial payments, or credit notes. Without it, there is no way to unambiguously refer to a particular line.

How to fix it

Add a cbc:ID element to each cac:InvoiceLine (or cac:CreditNoteLine) with a unique line identifier (e.g. 1, 2, 3).

Common causes

• The cbc:ID element is missing from one or more cac:InvoiceLine elements.
• The line ID element is present but empty.
• A template or code generator skipped the ID assignment for some lines.
• The cbc:ID was accidentally nested inside a child element like cac:Item.

Example: before (broken)

<cac:InvoiceLine>
  <!-- cbc:ID is missing -->
  <cbc:InvoicedQuantity unitCode="C62">10</cbc:InvoicedQuantity>
  <cbc:LineExtensionAmount currencyID="EUR">500.00</cbc:LineExtensionAmount>
  <cac:Item>
    <cbc:Name>Widget A</cbc:Name>
  </cac:Item>
</cac:InvoiceLine>

Example: after (fixed)

<cac:InvoiceLine>
  <cbc:ID>1</cbc:ID>
  <cbc:InvoicedQuantity unitCode="C62">10</cbc:InvoicedQuantity>
  <cbc:LineExtensionAmount currencyID="EUR">500.00</cbc:LineExtensionAmount>
  <cac:Item>
    <cbc:Name>Widget A</cbc:Name>
  </cac:Item>
</cac:InvoiceLine>

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