suite/sale_payment_web/views/sale_views.xml

<?xml version="1.0" encoding="UTF-8" ?>
<odoo>

    <record id="view_order_form_inherit" model="ir.ui.view">
        <field name="name">sale.order.form.inherit</field>
        <field name="model">sale.order</field>
        <field name="inherit_id" ref="sale.view_order_form"/>
        <field name="groups_id" eval="[(4, ref('group_payment_web'))]"/>
        <field name="arch" type="xml">
            <xpath expr="//button[@name='action_draft']" position="after">
                <button name="action_payment_register" type="object" string="Register Payment"/>
            </xpath>
            <xpath expr="//field[@name='amount_total']" position="after">
                <field name="manual_amount_remaining" widget="monetary"/>
            </xpath>
            <xpath expr="//div[@name='button_box']" position="inside">
                <field name="manual_payment_ids" invisible="1"/>
                <button name="action_manual_payments" string="Manual Payments" type="object" class="oe_stat_button"
                        icon="fa-dollar" attrs="{'invisible':[('manual_payment_ids', '=', [])]}"/>
            </xpath>
        </field>
    </record>

</odoo>