using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {

        // Your example

        string keyToEncode="cart_items[0][name]";

        string valueToEncode="Fictional Product name with special characters like ()";

​

        string encodedItem= System.Net.WebUtility.UrlEncode(keyToEncode)+"="+ System.Net.WebUtility.UrlEncode(valueToEncode);

        Console.WriteLine("Key/Value pair encoded as {0}", encodedItem);

        Console.WriteLine("Key/Value pair decoded as {0}", System.Net.WebUtility.UrlDecode(encodedItem));

        // Our exact code from production

        var sortedDict = new SortedDictionary<string, string>();

        sortedDict.Add(keyToEncode, valueToEncode);

        // ...other key-value pair adding omitted

        var encodedDictionary = new SortedDictionary<string, string>();

        foreach ( var keyValuePair in sortedDict )

        {

            var encodedKey = System.Net.WebUtility.UrlEncode( keyValuePair.Key );

            var encodedValue = System.Net.WebUtility.UrlEncode( keyValuePair.Value );

​

            encodedDictionary.Add( encodedKey, encodedValue );

        }

        Console.WriteLine(string.Join("&", encodedDictionary.Select(x => x.Key + "=" + x.Value)));

    }

}