suite/sale_payment_deposit/views/sale_portal_templates.xml

<?xml version="1.0" encoding="UTF-8" ?>
<odoo>
    <template id="sale_order_portal_template_deposit" name="Sales Order Portal Template - Deposit" inherit_id="sale.sale_order_portal_template">
        <!-- Set payment amount here rather than overriding the controller -->
        <xpath expr="//div[1]" position="before">
            <t t-if="sale_order.has_to_be_paid(True)">
                <t t-set="amount" t-value="sale_order.amount_total_deposit or amount"/>
            </t>
        </xpath>
        <!-- Display the Deposit amount prominently -->
        <xpath expr="//t[@t-set='title']/h2" position="after">
            <h5 t-if="sale_order.amount_total_deposit"><b t-field="sale_order.amount_total_deposit"/> Deposit</h5>
        </xpath>
        <!-- Display the Deposit and Total when Signing -->
        <xpath expr="//div[@id='modalaccept']/div/form/main/p/ul/li[2]" position="after">
            <li t-if="sale_order.amount_total_deposit"><span>Deposit today of:</span> <b data-id="total_amount_deposit" t-field="sale_order.amount_total_deposit"/></li>
        </xpath>
        <!-- Display the Deposit when Paying -->
        <xpath expr="//div[@id='modalaccept']/div/div/main/p/ul/li[2]" position="replace">
            <li t-if="sale_order.amount_total_deposit"><span>For the deposit amount of:</span> <b data-id="total_amount_deposit" t-field="sale_order.amount_total_deposit"/></li>
            <li t-else=""><span>For an amount of:</span> <b data-id="total_amount" t-field="sale_order.amount_total"/></li>
        </xpath>
    </template>
</odoo>