[sandbox] unable to capture payload on server side.

Problem: unable to capture payload from notifications

Platform: ASP.NET

Successfully execute the following code and webhook was created.

public static async Task Main(string[] args)
{
    try
    {
        var rc = new RestClient(RINGCENTRAL_CLIENT_ID, RINGCENTRAL_CLIENT_SECRET);
        await rc.Authorize(RINGCENTRAL_USERNAME, RINGCENTRAL_EXTENSION, RINGCENTRAL_PASSWORD);
        await rc.Restapi().Subscription().Post(new CreateSubscriptionRequest
        {
            eventFilters = new[] { "/restapi/v1.0/account/~/extension/~/message-store" },
            deliveryMode = new NotificationDeliveryModeRequest
            {
                transportType = "WebHook",
                address = DELIVERY_ADDRESS
            }
        });
        Console.WriteLine("WebHook ready!");
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex.Message);
    }

    Console.Read();
}

Expected to capture (not exact, but similar) payload

{  "timestamp": "2018-10-07T12:05:00.408+0000",  "uuid": "b11c9430-9687-4498-b12b-3fcb470bfe04",  "event": "/restapi/v1.0/account/230919004/extension/230919004/message-store",  "subscriptionId": "9d38419f-645f-4ee3-a053-8cf1368c21c4",  "body": {    "extensionId": 230919004,    "lastUpdated": "2018-10-07T12:05:00.531+0000",    "changes": [      {        "type": "Fax",        "updatedCount": 0,        "newCount": 1      }    ]  }}

I am using the following code to handle both subscription creation and payload handling.

public void ProcessRequest(HttpContext context)
{
    string headers = string.Empty;
    foreach (var key in context.Request.Headers.AllKeys)
    {
        headers += key + "=" + context.Request.Headers[key] + Environment.NewLine;
    }
    context.Response.Write(context.Request.RequestType + " == " + headers);

    if (context.Request.Headers["Validation-Token"] != null)
        context.Response.Headers.Add("Validation-Token", context.Request.Headers["Validation-Token"]);

    using (StreamReader reader = new StreamReader(context.Request.InputStream))
    {
        context.Response.Write(reader.ReadToEnd()
    }
    context.Response.Write(context.Request);
}

Can some please help on this matter?