Add coupon code on order confirmation mail (to admin)

/**
 * Add used coupons to the order confirmation email
 */
function twstudio_add_payment_method_to_admin_new_order( $order, $is_admin_email ) {

    if ( $is_admin_email ) {
        if( $order->get_used_coupons() ) {
            $coupons_count = count( $order->get_used_coupons() );
            $i = 1;
            $coupons_list = '';
            foreach( $order->get_used_coupons() as $coupon) {
                $coupons_list .=  $coupon;
                if( $i < $coupons_count )
                    $coupons_list .= ', ';
                $i++;
            }
            echo '<p><strong>Kuponger brukt (' . $coupons_count . ') :</strong> ' . $coupons_list . '</p>';
        } 
    } 
}

add_action( 'woocommerce_email_after_order_table', 'twstudio_add_payment_method_to_admin_new_order', 15, 2 );