# BR-01 Specification identifier is required

An invoice shall carry a Specification identifier (BT-24) that names the syntax and business rules the document follows.

## Problem Description

> **ERROR**: EN 16931 core business rule (CEN)

## Context and Significance

This is an EN 16931 core rule, so it applies to every CIUS, including XRechnung, Peppol BIS and Factur-X/ZUGFeRD. BT-24 tells the recipient and the validator which specification the invoice claims to follow; the KoSIT validator selects its validation scenario from this value. The error usually appears when an export writes the invoice data but leaves the profile setting empty. For XRechnung, the value must also match the XRechnung URN (BR-DE-21).

## Solution

Add cbc:CustomizationID in UBL, or rsm:ExchangedDocumentContext/ram:GuidelineSpecifiedDocumentContextParameter/ram:ID in CII, with the identifier of the specification the invoice follows: urn:cen.eu:en16931:2017 for the core standard, urn:cen.eu:en16931:2017#compliant#urn:xeinkauf.de:kosit:xrechnung_3.0 for XRechnung 3.0, or urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0 for Peppol BIS Billing 3.0.

- [Validate XML](/en/xrechnung-validator?source=resource&rule=BR-01)
- [Convert invoice](/en/pdf-to-xrechnung?source=resource&rule=BR-01)

## Valid Examples

- BT-24 = urn:cen.eu:en16931:2017#compliant#urn:xeinkauf.de:kosit:xrechnung_3.0 (XRechnung 3.0)
- BT-24 = urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0 (Peppol BIS Billing 3.0)

## Invalid Examples

- cbc:CustomizationID element is missing entirely from the document

## Code Examples

### Valid XML
```
<cbc:CustomizationID>urn:cen.eu:en16931:2017#compliant#urn:xeinkauf.de:kosit:xrechnung_3.0</cbc:CustomizationID>
<cbc:ID>RE-2024-0001</cbc:ID>
```

### Invalid XML
```
<cbc:ID>RE-2024-0001</cbc:ID>
<cbc:IssueDate>2024-05-01</cbc:IssueDate>
```

## Affected Fields

- [BT-24 Specification identifier](/resources/xrechnung/bt-24-specification-identifier)

## Related Rules

- [BR-DE-21](/resources/kosit-validator-errors/br-de-21-specification-identifier-syntax)

## 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://docs.peppol.eu/poacc/billing/3.0/rules/ubl-tc434/)
- [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.