Use the ID element to specify the reference.

Italian Specifications

Element	Italian Specification
`ID`	`2.1.2 (DatiOrdineAcquisto)`
`IssueDate`	`2.1.8 (DatiDDT)`

Elements

Element	Description
`Invoice/InvoiceLine/DocumentReference/ID`	Specify the code.
`Invoice/InvoiceLine/DocumentReference/ID [@schemeID]`	Specify the type of document that is referenced.
`Invoice/InvoiceLine/DocumentReference/IssueDate`	Specify the issue date.

Restrictions

You must use one of the codes from the UNCL1153 list.

Example

<ubl:Invoice>
    <!-- Code omitted for clarity -->
    <cac:InvoiceLine>
        <!-- Code omitted for clarity -->
        <cac:DocumentReference>
            <cbc:ID schemeID="ON">PO987654</cbc:ID>
            <cbc:IssueDate>2024-05-02</cbc:IssueDate>
        </cac:DocumentReference>
        <cac:DocumentReference>
            <cbc:ID schemeID="AAK">DESP987654</cbc:ID>
            <cbc:IssueDate>2024-06-03</cbc:IssueDate>
        </cac:DocumentReference>
        <!-- Code omitted for clarity -->
    </cac:InvoiceLine>
    <!-- Code omitted for clarity -->
</ubl:Invoice>