# BR-DEX-12 Third party payment description is required

The Third party payment description (BT-DEX-003) must be provided when the THIRD PARTY PAYMENT group (BG-DEX-09) is present.

## Problem Description

> **ERROR**: XRechnung extension rule (KoSIT, BR-DEX) · XRechnung 3.0

## Context and Significance

This XRechnung Extension rule fires only in the Extension scenario, where the THIRD PARTY PAYMENT group (mapped to UBL cac:PrepaidPayment) is available.

## Solution

Add cbc:InstructionID inside cac:PrepaidPayment to describe the third party payment. If you do not model third party payments, do not emit the BG-DEX-09 group; the standard XRechnung CIUS profile has no such group.

- [Validate XML](/en/xrechnung-validator?source=resource&rule=BR-DEX-12)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&rule=BR-DEX-12)

## Valid Examples

- cac:PrepaidPayment with cbc:InstructionID "Care fund contribution"

## Invalid Examples

- cac:PrepaidPayment present but cbc:InstructionID missing

## Code Examples

### Valid XML
```
<cac:PrepaidPayment>
  <cbc:ID>subsidy</cbc:ID>
  <cbc:PaidAmount currencyID="EUR">20.00</cbc:PaidAmount>
  <cbc:InstructionID>Care fund contribution</cbc:InstructionID>
</cac:PrepaidPayment>
```

### Invalid XML
```
<cac:PrepaidPayment>
  <cbc:ID>subsidy</cbc:ID>
  <cbc:PaidAmount currencyID="EUR">20.00</cbc:PaidAmount>
</cac:PrepaidPayment>
```

## Affected Fields

- [BT-DEX-003 Third party payment description](/resources/xrechnung)
- [BG-DEX-09 Third party payment](/resources/xrechnung)

## Related Rules

- [BR-DEX-10](/resources/kosit-validator-errors/br-dex-10-third-party-payment-type-required)
- [BR-DEX-11](/resources/kosit-validator-errors/br-dex-11-third-party-payment-amount-required)

## Validation Tools

- [Official KoSIT Validator](https://github.com/itplr-kosit/validator): Run the official KoSIT validator with the XRechnung configuration to check EN 16931 and XRechnung rules.
- [Convert PDF to XRechnung](/pdf-to-xrechnung): Find validation errors during conversion and review each correction.

## Related Resources

- [Official Specification](https://xeinkauf.de/xrechnung/)
- [Test Suite](https://github.com/itplr-kosit/xrechnung-testsuite)
- [All validation errors](/resources/kosit-validator-errors): Overview of the EN 16931, XRechnung and Peppol validation rules explained here.