# BR-51 Card primary account number must be masked

In accordance with card payment security standards, the invoice shall never include a full card primary account number (BT-87); PCI rules allow at most the first 6 and last 4 digits.

## Problem Description

In accordance with card payment security standards, the invoice shall never include a full card primary account number (BT-87); PCI rules allow at most the first 6 and last 4 digits.

> **ERROR**: XRechnung 3.0

## Context and Significance

This rule comes from the EN16931 core semantic model enforced by the KoSIT XRechnung 3.0.2 Schematron, ensuring invoices carry the mandatory data needed for automated processing.

## Solution

Mask cac:CardAccount/cbc:PrimaryAccountNumberID so only the first 6 and last 4 digits remain, replacing the middle digits with a masking character.

- validate
- convert

## Valid Examples

- BT-87 = 401288******1881 (masked)

## Invalid Examples

- BT-87 = 4012888888881881 (full PAN exposed)

## Code Examples

### Valid XML
```
<cac:PaymentMeans>
  <cbc:PaymentMeansCode>48</cbc:PaymentMeansCode>
  <cac:CardAccount>
    <cbc:PrimaryAccountNumberID>401288******1881</cbc:PrimaryAccountNumberID>
    <cbc:NetworkID>VISA</cbc:NetworkID>
  </cac:CardAccount>
</cac:PaymentMeans>
```

### Invalid XML
```
<cac:PaymentMeans>
  <cbc:PaymentMeansCode>48</cbc:PaymentMeansCode>
  <cac:CardAccount>
    <cbc:PrimaryAccountNumberID>4012888888881881</cbc:PrimaryAccountNumberID>
    <cbc:NetworkID>VISA</cbc:NetworkID>
  </cac:CardAccount>
</cac:PaymentMeans>
```

## Affected Fields

- [BT-87 Payment card primary account number](/resources/xrechnung/bt-87-payment-card-primary-account-number)

## Related Rules

- [BR-49](/resources/kosit-validator-errors/br-49-payment-means-type-code-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.