Need some help with Paypal IPN

Hello, I am attempting to do IPN for the first time and really could use some help.
With my code below, I can sucessfully take a payment. I want to be able to use IPN to take appropriate action on if the transaction is a success.
The transaction is successful yet the user is redirected to the page which should be the failure page.
Any help would be great!

Here is a sample of the code I use to send to paypal:

Dim amount As Decimal = 0.5
        Dim orderId As String = 1002
        Dim siteName As String = "nice"
        Dim ReturnURL As String = "nice/store/Notify.aspx"
        Dim CancelledURL As String = "nice/store/Cancelled.aspx"

        ' Create the PayPal redirect location
        Dim redirect As String = ""
        redirect += "https://www.paypal.com/xclick/business=Scott@nice.com"
        redirect += "&item_name=" + siteName + " Order " + orderId
        redirect += "&item_number=" + orderId
        redirect += "&amount=" + [String].Format("{0:0.00} ", amount)
        redirect += "&currency=USD"
        redirect += "&return=http://" + ReturnURL
        redirect += "&cancel_return=http://" + CancelledURL

        ' Redirect to the payment page
        Response.Redirect(redirect)

The payment is successfull then we do the IPN set to the notify.aspx page. The following code is supposed to set a session with "OK" if the payment is varified and redirect to the thankyou.aspx. BUT even though the payment is good the user is direced to the cancelled.aspx


Here is the Notify.aspx code:

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        '-- Capture posted form values from PayPal
        Dim FormValues As String = Request.Form.ToString()

        ' Create the postback to PayPal to verify sent information
        Dim PostBackRequest As HttpWebRequest
        PostBackRequest = WebRequest.Create("https://www.paypal.com/cgi-bin/webscr")
        PostBackRequest.Method = "POST"
        PostBackRequest.ContentType = "application/x-www-form-urlencoded"
        Dim PostBackString As String = FormValues + "&cmd=_notify-validate"
        PostBackRequest.ContentLength = PostBackString.Length

        ' Send the postback reply to PayPal
        Dim PostBackWriter As StreamWriter
        PostBackWriter = New StreamWriter(PostBackRequest.GetRequestStream(), Encoding.ASCII)
        PostBackWriter.Write(PostBackString)
        PostBackWriter.Close()

        ' Receive final verification from PayPal
        Dim ResponseReader As StreamReader
        ResponseReader = New StreamReader(PostBackRequest.GetResponse().GetResponseStream())
        Dim ResponseString As String = ResponseReader.ReadToEnd()
        ResponseReader.Close()

        If ResponseString = "VERIFIED" Then
            'Set a flag and transfer to sales success page
            Session("Verified") = "OK"
            Response.Redirect("ThankYou.aspx")
        Else
            'Set flag and transfer to sales failure page
            Session("Verified") = ""
            Response.Redirect("Cancelled.aspx")
        End If


    End Sub


How can I debug this? What should I or what can i do to fix this?Start Free Trial