# PEPPOL-EN16931-R101

> Element Document reference can only be used for Invoice line object

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/peppol-en16931-r101

## Official rule text

Element Document reference can only be used for Invoice line object

## Why did my invoice fail PEPPOL-EN16931-R101?

On an invoice line, cac:DocumentReference is reserved exclusively for the invoiced object identifier (BT-128) and must not be repurposed for other reference types. This prevents the line-level DocumentReference from being overloaded with contract, order, or dispatch references that belong elsewhere in the model.

## Common causes

- A line uses cac:DocumentReference to carry an order or contract reference instead of BT-128.
- The DocumentReference has no schemeID or an inappropriate document type code, signalling non-object usage.
- Header-level reference elements were incorrectly copied down to the line as DocumentReference.

## How do I fix it?

```
Use line DocumentReference only for the invoiced object (BT-128), and move other references to header elements such as cac:OrderReference or cac:ContractDocumentReference.
```