WooCommerce: checkout page hook sample

functions.php

<?php
add_filter( 'woocommerce_review_order_before_payment', 'add_my_checkout_section' );

function add_my_checkout_section() {
	wc_print_notice( apply_filters( 'woocommerce_checkout_my_checkout_section', __( 'Want a phone call before you buy?', 'woocommerce' ) . ' <a href="#">' . __( 'Click here, we call you back!', 'woocommerce' ) . '</a>' ), 'notice' );
}