Im trying to extend pos receipt, when I append the code just as in pos_restaurant I write the following code:

<?xml version="1.0" encoding="UTF-8"?>
<templates id="template" xml:space="preserve">

    <t t-extend="XmlReceipt">
        <t t-jquery='.total' t-operation='append'>
            <barcode encoding="CODE128"><t t-esc="o.id"/></barcode>
        </t>
    </t>

    <t t-extend="BillReceipt">
        <t t-jquery='.cashier' t-operation='append'>
            <barcode encoding="CODE128"><t t-esc="o.ean_128"/></barcode>
        </t>
    </t>
</templates>
but I get the following error:
File "lxml.etree.pyx", line 3373, in lxml.etree._Validator.assert_ (src/lxml/lxml.etree.c:166352)
So then, I try to modify the view by hand to see if it modify the receipt point_of_sale.report_receipt view, but it doesnt change the pos receipt neither the printed one or the web receipt....

AssertionError: Document does not comply with schema