public void UpdateGatewayResult()

class MyPage : System.Web.UI.Page
{
   private void SetOrderComplete(Dynamicweb.eCommerce.Orders.Order order)
   {
       //Set complete
       order.Complete = true;

       //Remove from stock
       Dynamicweb.eCommerce.Products.Product.UpdateStock(order, Dynamicweb.eCommerce.Products.Product.OrderStockOperator.Negative);

       //Remove all earlier gateway problems from this order
       order.GatewayTransactionProblems.Clear();

       //Save all posted info
       XmlDocument formXML = new XmlDocument();
       XmlElement rootNode = formXML.CreateElement("result");
       formXML.AppendChild(rootNode);
       foreach (string formKey in HttpContext.Current.Request.Form.Keys)
       {
           try
           {
               XmlElement node = formXML.CreateElement(XmlConvert.EncodeName(formKey));
               node.InnerText = HttpContext.Current.Request.Form[formKey];
               rootNode.AppendChild(node);
           }
           catch (Exception ex)
           {
               //
           }
       }
       order.GatewayResult = formXML.OuterXml;

       //Save
       order.UpdateGatewayResult();
       order.Save();
   }
}