# BR-DE-15 Buyer reference must be provided

XRechnung requires a buyer reference.

## Problem Description

XRechnung requires a buyer reference.

> **ERROR**: XRechnung 3.0

## Context and Significance

This entry follows the XRechnung 3.0.2 Schematron rule semantics used by KoSIT validation.

## Solution

Fill BT-10 buyer reference, such as the Leitweg-ID for German public buyers.

- validate
- convert

## Valid Examples

- BT-10 Buyer reference is present and valid.

## Invalid Examples

- BT-10 Buyer reference is missing or invalid.

## Technical Details

### Affected Fields
BT-10 Buyer reference

## 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.