# BR-52

> Each Additional supporting document (BG-24) shall contain a Supporting document reference (BT-122).

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/br-52

## Official rule text

Each Additional supporting document (BG-24) shall contain a Supporting document reference (BT-122).

## Why did my invoice fail BR-52?

Each Additional supporting document group (BG-24) must carry a Supporting document reference (BT-122) that identifies the referenced document (e.g. a timesheet, contract, or attachment). Without this identifier the referenced or embedded document cannot be linked back to anything meaningful.

## Common causes

- cac:AdditionalDocumentReference was added (often to carry an embedded attachment) without its cbc:ID.
- An empty cbc:ID element was emitted.
- The reference identifier was placed in DocumentDescription instead of the ID.

## How do I fix it?

```
In cac:AdditionalDocumentReference add <cbc:ID>DOC-2026-001</cbc:ID> identifying the supporting document.
```