pos/pos_sequence_ref_number/views/pos_template.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2017 Jordi Ballester, Rafael Blasco, Ivan Yelizariev, Antonio Espinosa, Meyomesse Gilles
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->
<odoo>
    <data>
        <template id="pos_sequence_ref_number_assets_backend"
                  name="pos_sequence_ref_number_assets_backend"
                  inherit_id="point_of_sale.assets">
            <xpath expr="." position="inside">
                <script src="/pos_sequence_ref_number/static/src/js/main.js"
                        type="text/javascript"/>
                <script type="text/javascript"
                        src="/pos_sequence_ref_number/static/lib/moment.js"/>
            </xpath>
        </template>
    </data>
</odoo>