# BR-06 Seller name is required

An invoice shall contain the Seller name (BT-27), the full legal name under which the supplier is registered; a differing trading name belongs in BT-28.

## Problem Description

An invoice shall contain the Seller name (BT-27), the full legal name under which the supplier is registered; a differing trading name belongs in BT-28.

> **ERROR**: XRechnung 3.0

## Context and Significance

This is a core EN16931 rule; the buyer must be able to identify who issued the invoice, so the seller name cannot be omitted.

## Solution

Provide cac:AccountingSupplierParty/cac:Party/cac:PartyLegalEntity/cbc:RegistrationName with the seller’s name.

- validate
- convert

## Valid Examples

- BT-27 = Muster Handels GmbH — seller registration name populated

## Invalid Examples

- cac:PartyLegalEntity/cbc:RegistrationName is missing for the supplier party

## Code Examples

### Valid XML
```
<cac:AccountingSupplierParty>
  <cac:Party>
    <cac:PartyLegalEntity>
      <cbc:RegistrationName>Muster Handels GmbH</cbc:RegistrationName>
    </cac:PartyLegalEntity>
  </cac:Party>
</cac:AccountingSupplierParty>
```

### Invalid XML
```
<cac:AccountingSupplierParty>
  <cac:Party>
    <cac:PartyLegalEntity>
      <cbc:CompanyID>DE123456789</cbc:CompanyID>
    </cac:PartyLegalEntity>
  </cac:Party>
</cac:AccountingSupplierParty>
```

## Affected Fields

- [BT-27 Seller name](/resources/xrechnung/bt-27-seller-name)

## Related Rules

- [BR-07](/resources/kosit-validator-errors/br-07-buyer-name-required)
- [BR-08](/resources/kosit-validator-errors/br-08-seller-postal-address-required)

## 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.