Coupon code showing Freeshipping

add_filter('woocommerce_cart_totals_discount_amount', 'tzn_custom_woocommerce_cart_totals_discount_amount', 99, 99);
function tzn_custom_woocommerce_cart_totals_discount_amount($get_coupon_discount_amount, $coupon_code)
{
    $c = new WC_Coupon($coupon_code);
    $coupon_id = $c->id;
    $amount = $c->amount;
    $free_shipping = get_post_meta($coupon_id, 'free_shipping', true);
    if ($amount == 0 && $free_shipping == 'yes') {
        $get_coupon_discount_amount = __("Kostenloser Versand", "tzn");
    }
    return $get_coupon_discount_amount;
}