account_invoice_xrechnung/view/configuration_form.xml

<?xml version="1.0"?>
<!-- This file is part of the account-datev-module from m-ds for Tryton.
 The COPYRIGHT file at the top level of this repository contains the
 full copyright notices and license terms. -->
<data>

    <xpath expr="/form/separator[@id='invoice']" position="before">

        <separator id="xrechnung" colspan="4" string="ZUGFeRD - e-Invoice"/>
        <label name="xrechn_zugferd_report"/>
        <field name="xrechn_zugferd_report"/>
        <label name="xrechn_default"/>
        <field name="xrechn_default"/>

    </xpath>

</data>