# PEPPOL-EN16931-R004

> Specification identifier MUST begin with the value 'urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0' and follow the format rules for the identifier.

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/peppol-en16931-r004

## Official rule text

Specification identifier MUST begin with the value 'urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0' and follow the format rules for the identifier.

## Why did my invoice fail PEPPOL-EN16931-R004?

The Specification identifier (BT-24), carried in cbc:CustomizationID, must start with 'urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0' and follow the identifier format rules. This value declares the document conforms to the Peppol BIS Billing 3.0 customization of EN 16931 and drives which validation ruleset receivers apply.

## Common causes

- cbc:CustomizationID is missing or holds only the plain EN 16931 identifier without the Peppol compliant suffix.
- Typo, wrong version, or extra whitespace in the CustomizationID string.
- CustomizationID and ProfileID values were swapped.
- A sector-specific extension was used but its prefix does not begin with the required base string.

## How do I fix it?

```
Set the specification identifier exactly: <cbc:CustomizationID>urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0</cbc:CustomizationID>.
```