# BR-DE-16 Seller tax identifier must be provided for taxable VAT categories

When VAT categories S, Z, E, AE, K, G, L, or M are used, seller VAT/tax identification or tax representative VAT identification is required.

## Problem Description

When VAT categories S, Z, E, AE, K, G, L, or M are used, seller VAT/tax identification or tax representative VAT identification is required.

> **ERROR**: XRechnung 3.0

## Context and Significance

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

## Solution

Provide BT-31, BT-32, or the applicable tax representative VAT identifier.

- validate
- convert

## Valid Examples

- BT-31 Seller VAT identifier is present and valid.

## Invalid Examples

- BT-31 Seller VAT identifier is missing or invalid.

## Code Examples

### Valid XML
```
<!-- VAT category S is used, so the seller declares a VAT identifier -->
<cac:PartyTaxScheme>
  <cbc:CompanyID>DE123456789</cbc:CompanyID>
  <cac:TaxScheme><cbc:ID>VAT</cbc:ID></cac:TaxScheme>
</cac:PartyTaxScheme>
```

### Invalid XML
```
<!-- VAT category S used, but seller has no BT-31/BT-32 tax identifier -->
<cac:TaxCategory>
  <cbc:ID>S</cbc:ID>
  <cbc:Percent>19.00</cbc:Percent>
  <cac:TaxScheme><cbc:ID>VAT</cbc:ID></cac:TaxScheme>
</cac:TaxCategory>
```

## Affected Fields

- [BT-31 Seller VAT identifier](/resources/xrechnung/bt-31-seller-vat-identifier)
- [BT-32 Seller tax registration identifier](/resources/xrechnung/bt-32-seller-tax-registration-identifier)

## Related Rules

- [BR-CO-09](/resources/kosit-validator-errors/br-co-9-vat-identifier-must-have-iso-country-prefix)

## 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.