Use the InvoiceDocumentReference/ID sub-element of the BillingReference element to specify the invoice number,

Italian Specification

Detail	Value
Italian Specification	`2.1.6.2 (IdDocumento)`

Element

Element	Description
`Invoice/BillingReference/InvoiceDocumentReference/ID`	Specify the number of the previous e-invoice.

Restrictions

This element is required if you send an adjustment e-invoice or a credit note.

Example

The following example specifies INV22334455 for the Invoice ID:


<ubl:Invoice>
    <cac:BillingReference>
        <cac:InvoiceDocumentReference>
            <!-- Code omitted for clarity -->
            <cbc:ID>INV22334455</cbc:ID>
            <!-- Code omitted for clarity -->
        </cac:InvoiceDocumentReference>
    </cac:BillingReference>
</ubl:Invoice>