Woocommerce add coupon code in new order admin email

functions.php

<?php

add_filter('woocommerce_get_order_item_totals','cs_add_discount',10,3);
function cs_add_discount($total_rows, $order, $tax_display) {
    if ( $order->get_total_discount() > 0 ) {
        $coupons = $order->get_used_coupons();
        $total_rows['couponused'] = array(
                'label' => __( 'Coupon code:', 'woocommerce' ),
                'value' => '' . implode(",",$coupons), );
    }
    return $total_rows;
}