The QBXML

<?xml version="1.0" encoding="utf-8"?>
<?qbxml version="16.0"?>
<QBXML>
  <QBXMLMsgsRq onError="stopOnError">
    <InvoiceAddRq>
      <InvoiceAdd>
        <CustomerRef>
          <ListID>1</ListID>
        </CustomerRef>

        <InvoiceLineAdd>
          <ItemRef>
            <ListID>1</ListID>
          </ItemRef>
          <Desc>
            Some description of the line item
          </Desc>
          <Quantity>1.0</Quantity>
          <Rate>100.0</Rate>
        </InvoiceLineAdd>
      </InvoiceAdd>
    </InvoiceAddRq>
  </QBXMLMsgsRq>
</QBXML>