在.net中覆盖cookie的问题

任何时候我试图检索这个cookie后，他们通过我们的支付网关(重定向到一个不同的域，然后带用户回到我们的页面)cookie不持久:(

它的行为就像它根本没有从cookie中加载对象。

下面是我用来存储/恢复cookie的代码:

public static string Store(EIN ein)
    {
        HttpCookie cookie = new HttpCookie("test123")
        {
            // Set the expiry date of the cookie to 15 years
            Expires = DateTime.Now.AddYears(15)
        };
        Stream myStream = new MemoryStream();
        try
        {
            // Create a binary formatter and serialize the
            // myClass into the memorystream
            IFormatter formatter = new BinaryFormatter();
            formatter.Serialize(myStream, ein);
            // Go to the beginning of the stream and
            // fill a byte array with the contents of the
            // memory stream
            myStream.Seek(0, SeekOrigin.Begin);
            byte[] buffer = new byte[myStream.Length];
            myStream.Read(buffer, 0, (int)myStream.Length);
            // Store the buffer as a base64 string in the cookie
            cookie.Value = Convert.ToBase64String(buffer);
            cookie.Domain = "url.com";
            // Add the cookie to the current http context
            HttpContext.Current.Response.Cookies.Add(cookie);
        }
        finally
        {
            // ... and remember to close the stream
            myStream.Close();
        }
        return cookie.Path;
    }
    public static EIN Restore()
    {
        // Always remember to check that the cookie is not empty
        HttpCookie cookie = HttpContext.Current.Request.Cookies["test123"];
        if (cookie != null)
        {
            // Convert the base64 string into a byte array
            byte[] buffer = Convert.FromBase64String(cookie.Value);
            // Create a memory stream from the byte array
            Stream myStream = new MemoryStream(buffer);
            try
            {
                // Create a binary formatter and deserialize the
                // contents of the memory stream into MyClass
                IFormatter formatter = new BinaryFormatter();
                EIN streamedClass = (EIN)formatter.Deserialize(myStream);
                return streamedClass;
            }
            finally
            {
                // ... and as always, close the stream
                myStream.Close();
            }
        }
        return new EIN();
    }

任何帮助在这是非常感激!!

Domain=domain
   Optional.  The Domain attribute specifies the domain for which the
   cookie is valid.  An explicitly specified domain must always start
   with a dot.