PayPal IPN 侦听器保持“重试”HTTP 响应 500

问：

我的 IPN 侦听器在过去 6 个月中一直运行良好。不过，在上周，所有事务都在“重试”并导致 HTTP 500 响应。我没有更改 IPN 侦听器中的任何代码，也没有更改 PayPal 中的任何设置。我已经打电话给PayPal，他们说这不是问题。我的托管公司 1&1 Ionos 几乎不知道我在说什么。我的 IPN 侦听器代码如下。我的网站使用 Asp.Net/VB.Net..

Imports System.Net
Imports System.IO
Imports System.Web.Util
Imports System.Data.Common

Partial Class IPNListener
    Inherits System.Web.UI.Page

    Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load
        'Post back to either sandbox or live
        'Dim strURL As String = "https://www.sandbox.paypal.com/cgi-bin/webscr"
        Dim strURL As String = "https://www.paypal.com/cgi-bin/webscr"
        Dim req As HttpWebRequest = CType(WebRequest.Create(strURL), HttpWebRequest)

        'Set values for the request back
        req.Method = "POST"
        req.ContentType = "application/x-www-form-urlencoded"
        req.Proxy = New WebProxy("ntproxyus.lxa.perfora.net", 3128)

        Dim Param() As Byte = Request.BinaryRead(HttpContext.Current.Request.ContentLength)
        Dim strRequest As String = Encoding.ASCII.GetString(Param)
        strRequest = strRequest + "&cmd=_notify-validate"
        req.ContentLength = strRequest.Length

        'Send the request to PayPal and get the response
        Dim streamOut As StreamWriter = New StreamWriter(req.GetRequestStream(), Encoding.ASCII)
        streamOut.Write(strRequest)
        streamOut.Close()
        Dim streamIn As StreamReader = New StreamReader(req.GetResponse().GetResponseStream())
        Dim strResponse As String = streamIn.ReadToEnd()
        streamIn.Close()

        Dim qscoll As NameValueCollection = HttpUtility.ParseQueryString(strRequest)

        'Insert the paypal response
        Dim order As New orders
        order.InsertPaypalResponse(qscoll("txn_id"), qscoll("custom"), strRequest)

        If strResponse = "VERIFIED" Then
              order.UpdateOrderFromPaypal(qscoll("custom"), qscoll("txn_id"), qscoll("payment_status"))
        ElseIf strResponse = "INVALID" Then
            'log for manual investigation
            order.UpdateOrderFromPaypal(qscoll("custom"), qscoll("txn_id"), qscoll("payment_status"))
        Else
            'Response wasn't VERIFIED or INVALID, log for manual investigation
            order.UpdateOrderFromPaypal(qscoll("custom"), qscoll("txn_id"), qscoll("payment_status"))
        End If
    End Sub
End Class