# BR-DE-27 Seller phone should contain at least three digits

XRechnung warns when seller telephone (BT-42) contains fewer than three digits.

## Problem Description

XRechnung warns when seller telephone (BT-42) contains fewer than three digits.

> **WARNING**: XRechnung 3.0

## Context and Significance

Seller contact data is used by public buyers to resolve invoice questions without rejecting the document outright.

## Solution

Provide a real contact number with digits, or remove malformed placeholder values.

- validate
- convert

## Valid Examples

- BT-42 = +49 30 123456

## Invalid Examples

- BT-42 = --
- BT-42 = x

## Technical Details

### Affected Fields
BT-42 Seller contact telephone number

## Related Rules

- [BR-DE-6](/resources/kosit-validator-errors/br-de-6-seller-name-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.