Flux checkout - reposition coupon form.

functions.php

<?php 
/**
 * Flux checkout -  reposition coupon form.
 *
 * @return void
 */
function flux_reposition_coupon_form() {
	remove_action( 'woocommerce_review_order_after_cart_contents', array( 'Iconic_Flux_Sidebar', 'checkout_add_coupon_form' ), 9 );
	add_action( 'woocommerce_review_order_before_payment', array( 'Iconic_Flux_Sidebar', 'checkout_add_coupon_form' ) );
}
add_action( 'init', 'flux_reposition_coupon_form', 20 );