Paynet switch Odoo order ref with customer order ref

Reading the specs it seemed to be the other way around.
But it has been confirmed by someone at SIX. That the reference for
linked sale order must be the customer order reference.

ebill_paynet/messages/invoice-2003A.xml

@@ -35,12 +35,14 @@
           </REFERENCE-DATE>
         </INVOICE-REFERENCE>
         {% for order in invoice_line.sale_line_ids.mapped('order_id') %}
+        {%- if order.client_order_ref %}
         <ORDER>
           <REFERENCE-DATE>
-            <Reference-No>{{ order.name }}</Reference-No>
+            <Reference-No>{{ order.client_order_ref }}</Reference-No>
             <Date Format="CCYYMMDD">{{ format_date(order.date_order) }}</Date>
           </REFERENCE-DATE>
         </ORDER>
+        {%- endif %}
         {% endfor %}
       </REFERENCE>
       <BILLER>

ebill_paynet/tests/examples/invoice_b2b.xml

@@ -35,9 +35,8 @@
           </REFERENCE-DATE>
         </INVOICE-REFERENCE>
         <ORDER>
-          <!-- TODO add linked sale order in test -->
           <REFERENCE-DATE>
-            <Reference-No>Order123</Reference-No>
+            <Reference-No>CustomerRef</Reference-No>
             <Date Format="CCYYMMDD">20190601</Date>
           </REFERENCE-DATE>
         </ORDER>