# PEPPOL-EN16931-R080

> Only one project reference is allowed on document level

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/peppol-en16931-r080

## Official rule text

Only one project reference is allowed on document level

## Why did my invoice fail PEPPOL-EN16931-R080?

At most one Project reference (BT-11) may appear at the document (invoice) level. EN 16931 models the project reference as a single business term, so multiple ProjectReference elements on the header are not permitted.

## Common causes

- The invoice carries several cac:ProjectReference elements at document level instead of one.
- Multiple project identifiers from different source systems were all mapped to header ProjectReference.
- A per-line project code was mistakenly duplicated onto the document header.

## How do I fix it?

```
Keep a single header reference: <cac:ProjectReference><cbc:ID>PRJ-2026-17</cbc:ID></cac:ProjectReference> and remove any additional ProjectReference elements.
```