# PEPPOL-EN16931-R003

Source: https://xmlvalid.com/rules/PEPPOL-EN16931-R003

> A buyer reference or purchase order reference MUST be provided.

- Level: error
- Rule sets: Peppol BIS Billing 3.0 rules 3.0.21
- Context: `ubl-creditnote:CreditNote | ubl-invoice:Invoice`
- Test: `cbc:BuyerReference or cac:OrderReference/cbc:ID`

## Why it fails

- Neither `cbc:BuyerReference` nor `cac:OrderReference/cbc:ID` is given. Buyers use one of them to match the invoice to a purchase.

## How to fix it

- Add the reference the buyer gave you as `cbc:BuyerReference` (BT-10), or the purchase order number as `cac:OrderReference/cbc:ID` (BT-13).

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