Dear,
I custom payment gateway depend on KenticoCMS_EcommerceGuide_Purchase process and payment gateways_Developing custom payment gateways. I using PayPal payment method
I create custom payment gateway form and custom payment gateway class, in shopping cart process, at step 6 of shopping cart process when payment gateway form show, I click "Finish Payment" button
and it redirect to https://www.sandbox.paypal.com/us/cgi-bin/webscr with parametter of URL: https://www.sandbox.paypal.com/cgi-bin/webscr?cardnumber=4991319512885564&price=25.289&currency=USD&orderid=29
but paypay is not recognize my order, it isn't minus money in my account and don't have this order
This is my code:
Payment gateway form:

public partial class Doggy_PaymentProvider_CustomPaypalGatewayForm : CMSPaymentGatewayForm
{
protected void Page_Load(object sender, EventArgs e)
{
lblTitle.Text = "Your credit card details";
lblCardNumber.Text = "Credit card number:";
}
public override void LoadData()
{
base.LoadData();
txtCardNumber.Text = ValidationHelper.GetString(this.ShoppingCartInfoObj.PaymentGatewayCustomData["CustomGatewayCardNumber"], "");
}
public override string ValidateData()
{
return base.ValidateData();
if (txtCardNumber.Text.Trim() == "")
{
lblError.Visible = true;
lblError.Text = "Please enter your credit card number";
return lblError.Text;
}
return "";
}
public override string ProcessData()
{
this.ShoppingCartInfoObj.PaymentGatewayCustomData["CustomGatewayCardNumber"] = txtCardNumber.Text.Trim();
return "";
}
}

Custom payment gateway class:
namespace Doggy.PaymentProvider
{
public class PaypalPaymentGateway : CMSPaymentGatewayProvider
{
public PaymentResultInfo PaypalPaymentResult;

public override CMSPaymentGatewayForm GetPaymentDataForm()
{
try
{
return (CMSPaymentGatewayForm)this.ShoppingCartControl.LoadControl("~/Doggy/PaymentProvider/CustomPaypalGatewayForm.ascx");
}
catch
{
return null;
}
}
public override void ProcessPayment()
{
// Get payment gateway url
string url = this.GetPaymentGatewayUrl();
if (url != "")
{
// Initialize payment parameters
Hashtable parameters = InitializePaymentParameters();
// Add required payment data to the url
url = GetFullPaymentGatewayUrl(url, parameters);
// Redirect to payment gateway to finish payment
this.ShoppingCartControl.Page.Response.Redirect(url);
}
else
{
// Show error message - payment gateway url not found
this.ErrorMessage = "Unable to finish payment: Payment gateway url not found.";
// Update payment result
this.PaypalPaymentResult.PaymentDescription = this.ErrorMessage;
this.PaypalPaymentResult.PaymentIsCompleted = false;
// Update order payment result in database
this.UpdateOrderPaymentResult();
}
}

/// <summary>
/// Returns table with initialized payment parameters.
/// </summary>
/// <returns></returns>
private Hashtable InitializePaymentParameters()
{
Hashtable parameters = new Hashtable();
parameters["orderid"] = this.ShoppingCartInfoObj.OrderId;
parameters["price"] = this.ShoppingCartInfoObj.TotalPrice;
parameters["currency"] = this.ShoppingCartInfoObj.CurrencyInfoObj.CurrencyCode;
parameters["cardnumber"] = Convert.ToString(this.ShoppingCartInfoObj.PaymentGatewayCustomData["CustomGatewayCardNumber"]);

return parameters;
}

/// <summary>
/// Returns payment gateway url with payment data in query string.
/// </summary>
/// <param name="url">Payment gateway url.</param>
/// <param name="parameters">Initialized payment paremeters.</param>
/// <returns></returns>
private string GetFullPaymentGatewayUrl(string url, Hashtable parameters)
{
foreach (DictionaryEntry parameter in parameters)
{
// Add payment data to the url
url = UrlHelper.AddParameterToUrl(url, Convert.ToString(parameter.Key), HttpUtility.UrlEncode(Convert.ToString(parameter.Value)));
}
return url;
}

}
}

Please help me how to custom payment gateway correct and which param I need to get