Show a custom checkbox before the "Place Order" button on the checkout page if the cart contains deposit items.

functions.php

<?php
// Add the required checkbox right before the "Place Order" button
// plugin: https://www.codeixer.com/woocommerce-deposits-plugin/
add_action('woocommerce_review_order_before_submit', 'custom_checkout_terms_checkbox', 9);
function custom_checkout_terms_checkbox() {
	if(!cidw_cart_have_deposit_item()){
		return;
	}
    ?>
    <p class="form-row terms-field" style="margin-bottom: 15px;">
        <label class="woocommerce-form__label woocommerce-form__label-for-checkbox">
            <input type="checkbox" class="woocommerce-form__input woocommerce-form__input-checkbox" name="custom_terms" id="custom_terms"> 
           I agree to the <strong><a href="#" target="_blank">Deposits Terms & Conditions</a></strong>.
        </label>
    </p>
    <?php
}

// Validate the checkbox before order submission
add_action('woocommerce_checkout_process', 'custom_checkout_validate_terms_checkbox');
function custom_checkout_validate_terms_checkbox() {
	if(!cidw_cart_have_deposit_item()){
		return;
	}
    if (!isset($_POST['custom_terms'])) {
        wc_add_notice(__('You must agree to the Deposit Terms & Conditions before placing your order.'), 'error');
    }
}