Unable to integrate payment gateway of axis easy pay in c#.net

protected void Redirect_Click(object sender, EventArgs e)
        {

            //1. URL
            string TranUrl = "https://uat-etendering.axisbank.co.in/easypay2.0/frontend/index.php/api/payment";

            //2. method to generate Checksum value. //CID + RID + CRN  + AMT + "axis";

            String strCID = string.Empty;
            String strRID = string.Empty;
            String strCRN = string.Empty;
            String strAMT = string.Empty;
            String strName = string.Empty;
            String strClass = string.Empty;
            String strRoll = string.Empty;
            strCID = "5000"; // update the same as assigned by AxisBank
            strRID = Generatetxnid();
            strCRN = Generatetxnid();
            strAMT = TextBox4.Text;
            strName = TextBox1.Text;
            strRoll = TextBox3.Text;
            strClass = TextBox2.Text;
           
            string StrCheckSumString = strCID + strRID + strCRN  + strAMT + "axis";

            string Checksum = sha256_hash(StrCheckSumString);
            //Sample values has been passed in each parameter. Please update with your values.
            string PlainText = "CID=" + strCID + "&RID=" + strRID + "&CRN=" + strCRN + "&AMT=" + TextBox4.Text + "&VER=1.0&TYP=TEST&CNY=INR&RTU=http://localhost:50864/Default.aspx/&PPI=A01/2554-trid|A01/2554|05/21/2016 12:39:14&RE1=MN&RE2=&RE3=&RE4=&RE5=&CKS=" + Checksum;

            string encryptedstring = Encrypt(PlainText, "axisbank12345678");
            //Correct Value with checksum.
            
            NameValueCollection data = new NameValueCollection();
            data.Add("i", encryptedstring);
            
            RedirectAndPOST(this.Page, TranUrl, data);

        }
        private static String PreparePOSTForm(string url, NameValueCollection data)
        {
            try
            {
                //Set a name for the form
                string formID = "PostForm";

                //Build the form using the specified data to be posted.
                StringBuilder strForm = new StringBuilder();
                strForm.Append("");
                foreach (string key in data)
                {
                    strForm.Append("");
                }
                strForm.Append("");

                //Build the JavaScript which will do the Posting operation.
                StringBuilder strScript = new StringBuilder();
                strScript.Append("");
                strScript.Append("var v" + formID + " = document." + formID + ";");
                strScript.Append("v" + formID + ".submit();");
                strScript.Append("");

                //Return the form and the script concatenated. (The order is important, Form then JavaScript)
                return strForm.ToString() + strScript.ToString();

            }
            catch (Exception)
            {

                throw;
            }
        }
        private void RedirectAndPOST(Page page, string TranUrl, NameValueCollection data)
        {
            try
            {

                //Prepare the Posting form
                string strForm = PreparePOSTForm(TranUrl, data);
                //Add a literal control the specified page holding the Post Form, this is to submit the Posting form with the request.
                page.Controls.Add(new LiteralControl(strForm));



            }
            catch

            { }
        }

        public string Encrypt(string input, string key)
        {
            byte[] keyArray = UTF8Encoding.UTF8.GetBytes(key);
            byte[] toEncryptArray = UTF8Encoding.UTF8.GetBytes(input);
            Aes kgen = Aes.Create("AES");
            kgen.Mode = CipherMode.ECB;
            //kgen.Padding = PaddingMode.None;
            kgen.Key = keyArray;
            ICryptoTransform cTransform = kgen.CreateEncryptor();
            byte[] resultArray = cTransform.TransformFinalBlock(toEncryptArray, 0, toEncryptArray.Length);
            return Convert.ToBase64String(resultArray, 0, resultArray.Length);
        }
        public static String sha256_hash(String value)
        {
            StringBuilder Sb = new StringBuilder();
            using (SHA256 hash = SHA256Managed.Create())
            {
                Encoding enc = Encoding.UTF8;
                Byte[] result = hash.ComputeHash(enc.GetBytes(value));
                foreach (Byte b in result)
                    Sb.Append(b.ToString("x2"));
            }
            return Sb.ToString();
        }