# PEPPOL-EN16931-R004

Source: https://xmlvalid.com/rules/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.

- Level: error
- Rule sets: Peppol BIS Billing 3.0 rules 3.0.21
- Context: `ubl-creditnote:CreditNote | ubl-invoice:Invoice`
- Test: `starts-with(normalize-space(cbc:CustomizationID/text()), 'urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0') and not(contains(normalize-space(cbc:CustomizationID/text()), '::'))`

## Why it fails

- `cbc:CustomizationID` is not the Peppol BIS Billing 3.0 identifier, for example plain `urn:cen.eu:en16931:2017` or an XRechnung identifier sent over Peppol.

## How to fix it

- Use `urn:cen.eu:en16931:2017#compliant#urn:fdc:peppol.eu:2017:poacc:billing:3.0` (an extension of it may follow, but it must begin with this).

Validate a document against these rules: https://xmlvalid.com/validate