# PEPPOL-EN16931-R080

Source: https://xmlvalid.com/rules/PEPPOL-EN16931-R080

> Only one project reference is allowed on document level

- Level: error
- Rule sets: Peppol BIS Billing 3.0 rules 3.0.21
- Context: `ubl-creditnote:CreditNote`
- Test: `(count(cac:AdditionalDocumentReference[cbc:DocumentTypeCode='50']) <= 1)`

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