# BR-DE-13 Buyer reference must be provided

The buyer reference must be provided on the invoice.

## Problem Description

The buyer reference must be provided on the invoice.

> **ERROR**: XRechnung 3.0

## Context and Significance

The buyer reference is used by many public sector recipients to route the invoice internally (department, cost center, order reference) and to match it to the procurement process. If you do not have an order reference, use the identifier provided by the buyer/portal.

## Solution

Add the buyer reference to the invoice.

## Valid Examples

- DEPT-4711
- PO-2025-000123
- Buyer-provided routing reference

## Invalid Examples

- Missing buyer reference
- Using a seller internal reference instead

## Code Examples

### Valid XML
```
<cbc:BuyerReference>PO-2025-000123</cbc:BuyerReference>
```

### Invalid XML
```
<!-- Missing cbc:BuyerReference -->
```

## Technical Details

### Affected Fields
Buyer Reference

## Related Rules

- [BR-DE-15](/resources/kosit-validator-errors/br-de-15-leitweg-id-must-be-provided)

## Validation Tools

- [Official KoSIT Validator](https://erechnungsvalidator.service-bw.de/): Validate your XRechnung files against all BR-DE rules.
- [Convert PDF to XRechnung](/pdf-to-xrechnung): Automatic validation error fixes when converting.

## Related Resources

- [Official Specification](https://xeinkauf.de/xrechnung/)
- [Test Suite](https://github.com/itplr-kosit/xrechnung-testsuite)
- [Complete Error List](/resources/kosit-validator-errors): Overview of all German XRechnung validation rules.