# UBL-CR-666

> A UBL invoice shall not include an AdditionalDocumentReference simultaneously referring an Invoice Object Identifier and an Attachment

Checked against Peppol BIS Billing 3.0 2026.5

Canonical: https://einvoicecheck.eu/rules/ubl-cr-666

## Official rule text

A UBL invoice shall not include an AdditionalDocumentReference simultaneously referring an Invoice Object Identifier and an Attachment