If a Purchase Order exists, you can include it in your PEPPOL Document.

PEPPOL requies that you specify an Order Reference as described here or a Buyer Reference as described in the PEPPOL Buyer Reference.

Generally, most recipients have a unique ID that they use to identify an order. You can use this if you like.

Use the ID subelement of the OrderReference element to specify this information.

Example

<Invoice>
    <!-- code omitted for clarity -->
    <cac:OrderReference>
        <cbc:ID>PO-11223344</cbc:ID>
    </cac:OrderReference>    
    <!-- code omitted for clarity -->
</Invoice>