pos/pos_session_pay_invoice/views/pos_session.xml

<?xml version="1.0" encoding="UTF-8" ?>
<odoo>
    <record id="view_pos_config_kanban" model="ir.ui.view">
       <field name="name">pos.config.kanban.view</field>
        <field name="model">pos.config</field>
        <field name="inherit_id" ref="point_of_sale.view_pos_config_kanban"/>
        <field name="arch" type="xml">
            <button name="open_ui" position="after">
                <button t-if="record.current_session_state.raw_value === 'opened'"
                        class="btn btn-info"
                        name="open_existing_session_cb"
                        type="object">Summary</button>
            </button>
        </field>
    </record>

    <record id="view_pos_session_form" model="ir.ui.view">
        <field name="name">pos.session.form.view</field>
        <field name="model">pos.session</field>
        <field name="inherit_id" ref="point_of_sale.view_pos_session_form"/>
        <field name="arch" type="xml">
            <button name="open_cashbox" position="after">
                <button class="oe_stat_button" name="%(action_pos_invoice_in)d"
                        type="action" icon="fa-level-up"
                        attrs="{'invisible':['|','|',('cash_control', '=', False),('state', 'not in', ['opened', 'closing_control']), ('statement_ids', '=', False)]}">
                    <div class="o_form_field o_stat_info">
                        <span class="o_stat_text">Pay</span>
                        <span class="o_stat_text">Invoice</span>
                    </div>
                </button>
                <button class="oe_stat_button" name="%(action_pos_invoice_out)d"
                        type="action" icon="fa-level-down"
                        attrs="{'invisible':['|',('state', 'not in', ['opened', 'closing_control']), ('statement_ids', '=', False)]}">
                    <div class="o_form_field o_stat_info">
                        <span class="o_stat_text">Collect Payment</span>
                        <span class="o_stat_text">from Invoice</span>
                    </div>
                </button>

            </button>
        </field>
    </record>
</odoo>