اینم کدهای صفحه صلی
namespace BankMellat_WebForms
{
    public partial class _default : System.Web.UI.Page
    {
        public static readonly string PgwSite = ConfigurationManager.AppSettings["PgwSite"];
        public static readonly string CallBackUrl = ConfigurationManager.AppSettings["CallBackUrl"];
        public static readonly string TerminalId = ConfigurationManager.AppSettings["TerminalId"];
        public static readonly string UserName = ConfigurationManager.AppSettings["UserName"];
        public static readonly string UserPassword = ConfigurationManager.AppSettings["UserPassword"];
        void BypassCertificateError()
        {
            ServicePointManager.ServerCertificateValidationCallback +=
                delegate(
                    Object sender1,
                    X509Certificate certificate,
                    X509Chain chain,
                    SslPolicyErrors sslPolicyErrors)
                {
                    return true;
                };
        }
        public static string RefId = "";
        public string SetDefaultDate()
        {
            return DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString().PadLeft(2, '0') + DateTime.Now.Day.ToString().PadLeft(2, '0');

        }
        public string SetDefaultTime()
        {
            return DateTime.Now.Hour.ToString().PadLeft(2, '0') + DateTime.Now.Minute.ToString().PadLeft(2, '0') + DateTime.Now.Second.ToString().PadLeft(2, '0');
        }
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void btnpayment_Click(object sender, EventArgs e)
        {
            //get values from form
            string _name = txtname.Text;
            string _email = txtemail.Text;
            string __amount = txtamount.Text;
            int _amount = int.Parse(__amount);
            //save record to database
            int? record_id = 0;
            var db = new dbDataContext();
            db.InsertPayment(_name, _email, _amount, "پرداخت نشده", ref record_id);
            //==========================================================================
            try
            {
                string result = "";
                BypassCertificateError();
                BankMellat.PaymentGatewayClient bp = new BankMellat.PaymentGatewayClient();
                result = bp.bpPayRequest(Int64.Parse(TerminalId), UserName, UserPassword, long.Parse(record_id.Value.ToString()), _amount, SetDefaultDate(), SetDefaultTime(), "irarzan.ir", CallBackUrl, 0);
                string[] res = result.Split(',');
                if (res[0] == "0")
                {
                    db.UpdatePayment("پرداخت نشده", res[1], "", record_id);
                    ClientScript.RegisterStartupScript(typeof(Page), "clientscript", "<script>postRefId('" + res[1] + "')</script>");
                }
                else
                {
                    msglabel.Text = "خطای " + res[0] + " در ارتباط با بانک";
                }
            }
            catch
            {
                msglabel.Text = "خطا در ارتباط با بانک";
            }
            //==========================================================================

        }
    }
}

اینم کد های صفحه payment

namespace BankMellat_WebForms
{
    public partial class payment : System.Web.UI.Page
    {
        public static readonly string PgwSite = ConfigurationManager.AppSettings["PgwSite"];
        public static readonly string CallBackUrl = ConfigurationManager.AppSettings["CallBackUrl"];
        public static readonly string TerminalId = ConfigurationManager.AppSettings["TerminalId"];
        public static readonly string UserName = ConfigurationManager.AppSettings["UserName"];
        public static readonly string UserPassword = ConfigurationManager.AppSettings["UserPassword"];
        void BypassCertificateError()
        {
            ServicePointManager.ServerCertificateValidationCallback +=
                delegate(
                    Object sender1,
                    X509Certificate certificate,
                    X509Chain chain,
                    SslPolicyErrors sslPolicyErrors)
                {
                    return true;
                };
        }
        public static string RefId = "";
        public string SetDefaultDate()
        {
            return DateTime.Now.Year.ToString() + DateTime.Now.Month.ToString().PadLeft(2, '0') + DateTime.Now.Day.ToString().PadLeft(2, '0');

        }
        public string SetDefaultTime()
        {
            return DateTime.Now.Hour.ToString().PadLeft(2, '0') + DateTime.Now.Minute.ToString().PadLeft(2, '0') + DateTime.Now.Second.ToString().PadLeft(2, '0');
        }
        protected void Page_Load(object sender, EventArgs e)
        {
            if (Request.Params["ResCode"] != null)
            {
                string _rescode = Request.Params["ResCode"];
                string _refid = Request.Params["RefId"];
                string _saleorderid = Request.Params["SaleOrderId"];
                string _salerefrenceid = Request.Params["SaleRefrenceId"];
                if (_rescode == "0")
                {
                    string result = "";
                    BypassCertificateError();
                    BankMellat.PaymentGatewayClient bp = new BankMellat.PaymentGatewayClient();
                    result = bp.bpVerifyRequest(Int64.Parse(TerminalId), UserName, UserPassword, long.Parse(_saleorderid), long.Parse(_saleorderid), long.Parse(_salerefrenceid));
                    if (result == "0")
                    {
                        var db = new dbDataContext();
                        var payment_id = db.tblPayments.Where(c => c.RefID == _refid).Single();
                        db.UpdatePayment("پرداخت شده", _refid, _salerefrenceid, payment_id.id);
                        msglabel.Text = "پرداخت شما با موفقیت انجام شد" + "<br />" + "شماره پیگیری تراکنش: " + _salerefrenceid;
                    }
                    else
                    {
                        msglabel.Text = "پرداخت آنلاین با خطا مواجه شده است.";
                    }
                }
                else
                {
                    msglabel.Text = "پرداخت آنلاین با خطا مواجه شده است.";
                }
            }
        }
    }
}