using System;
using System.Collections.Generic;
using System.Security.Cryptography;
using System.Web;

public class Program
{
    public static void Main()
    {
        var parameters = new Dictionary<string, string>
        {
            { "bankId", "507f1f77bcf86cd799439011" },
            { "amount", "500" },
            { "userId", "987654" },
            { "name", "Test User" },
            { "userName", "testUserName" },
            { "processId", "123456789" }
        };

        var paramString = HttpUtility.ParseQueryString(string.Empty);
        foreach (var param in parameters)
        {
            paramString[param.Key] = param.Value;
        }

        string encodedParams = paramString.ToString(); // bankId=507f1f77bcf86cd799439011&amount=500&userId=987654&name=Test+User&userName=testUserName&processId=123456789
        string key = "e59de9db1246eef0423a8c9045bdc5c9ea5729695cf792d065cac10373add831"; // Replace it with your own API Secret.
        string sign = CreateToken(encodedParams, key); // E2ftNgJbcRAEZfWA9Lb8SbhsB7fBS8UJZMVOwRMslr4=
    }

    static string CreateToken(string message, string secret)
    {
        secret = secret ?? "";
        var encoding = new System.Text.ASCIIEncoding();
        byte[] keyByte = encoding.GetBytes(secret);
        byte[] messageBytes = encoding.GetBytes(message);
        using (var hmacsha256 = new HMACSHA256(keyByte))
        {
            byte[] hashmessage = hmacsha256.ComputeHash(messageBytes);
            return Convert.ToBase64String(hashmessage);
        }
    }
}