# UBL-SR-56

Source: https://xmlvalid.com/rules/UBL-SR-56

> An Invoice shall contain maximum one Originator document reference identifier (BT-17).

- Level: error
- Rule sets: EN 16931 rules (UBL) 1.3.17, EN 16931 rules 1.3.16 (UBL), EXTENDED-CTC-FR rules (UBL) 1.4.0.04
- Context: `/ubl:Invoice | /cn:CreditNote`
- Test: `count(cac:OriginatorDocumentReference/cbc:ID) <= 1`

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