# BR-CO-26 Seller must be identifiable by an identifier, legal registration ID, or VAT ID

To allow the buyer to identify the supplier automatically, at least one of Seller identifier (BT-29), Seller legal registration identifier (BT-30) or Seller VAT identifier (BT-31) must be present.

## Problem Description

To allow the buyer to identify the supplier automatically, at least one of Seller identifier (BT-29), Seller legal registration identifier (BT-30) or Seller VAT identifier (BT-31) must be present.

> **ERROR**: XRechnung 3.0

## Context and Significance

Buyer ERP systems automatically match suppliers by these identifiers. If none is present, the invoice falls into a manual matching queue and payment is delayed.

## Solution

Populate at least one of BT-29, BT-30 or BT-31 in the Seller party block.

- validate
- convert

## Valid Examples

- BT-31 = "DE123456789"
- BT-30 = "HRB 12345"
- BT-29 = "GLN 4012345000094"

## Invalid Examples

- Seller party with name and address only, BT-29/BT-30/BT-31 all absent
- BT-31 cleared because the seller is not VAT-registered, but BT-30 also missing

## Technical Details

### Affected Fields
BT-29 Seller identifier, BT-30 Seller legal registration identifier, BT-31 Seller VAT identifier

## Related Rules

- [BR-CO-9](/resources/kosit-validator-errors/br-co-9-vat-identifier-must-have-iso-country-prefix)
- [BR-DE-7](/resources/kosit-validator-errors/br-de-7-buyer-name-must-be-provided)
- [BR-DE-8](/resources/kosit-validator-errors/br-de-8-value-added-tax-point-date-code-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.