pos/pos_payment_terminal_server/views/pos_config.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2019 ACSONE SA/NV
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->

<odoo>

    <record model="ir.ui.view" id="pos_config_form_view">
        <field name="name">pos.config.form (in pos_payment_multi_terminal)</field>
        <field name="model">pos.config</field>
        <field name="inherit_id" ref="point_of_sale.view_pos_config_form"/>
        <field name="arch" type="xml">
            <field name="iface_cashdrawer" position="after">
                <field name="use_payment_terminal_server"/>
                <field name="iface_payment_terminal_server"
                       placeholder="http://localhost:8070"
                       attrs="{'required': [('use_payment_terminal_server', '!=', False)], 'invisible': [('use_payment_terminal_server', '=', False)]}"/>
                <field name="iface_payment_terminal_id"
                       attrs="{'required': [('use_payment_terminal_server', '!=', False)], 'invisible': [('use_payment_terminal_server', '=', False)]}"/>
            </field>
        </field>
    </record>

</odoo>