contract/contract_sale_payment_mode/views/res_config_settings.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- Copyright 2020 ACSONE SA/NV
     License AGPL-3.0 or later (http://www.gnu.org/licenses/agpl). -->

<odoo>

    <record model="ir.ui.view" id="res_config_settings_form_view">
        <field name="model">res.config.settings</field>
        <field name="inherit_id" ref="sale.res_config_settings_view_form"/>
        <field name="arch" type="xml">
            <xpath expr="//div[@id='sale_config_online_confirmation_sign']"
                   position="before">
                <div class="col-12 col-lg-6 o_setting_box"
                     id="specific_contract_payment_mode">
                    <div class="o_setting_left_pane">
                        <field name="specific_contract_payment_mode"/>
                    </div>
                    <div class="o_setting_right_pane">
                        <label for="specific_contract_payment_mode"/>
                        <span class="fa fa-lg fa-building-o"
                              title="Values set here are company-specific."
                              groups="base.group_multi_company"/>
                        <div class="text-muted">
                            This option allow allow to set different payment mode for the contracts generated from the sale order than the one will be used for invoices.
                        </div>
                    </div>
                </div>
            </xpath>
        </field>
    </record>



</odoo>