La página de HomeControler / Index.cshtml es la siguiente

<div id="paypalDiv">

        <form id="paypalForm" action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
            <fieldset>
                <p class="inline-small-label" style="padding-top: 7px;">
                    <label for="device-id"><span>User ID</span></label></p>

                <input id="custom" class="full-width" type="text" name="custom" value="">
                <input class="full-width" type="hidden" name="business" value="[email protected]">
                <input type="hidden" name="cmd" value="_xclick">
                <input type="hidden" name="item_name" value="credits">
                <input type="hidden" name="item_number" value="40">
                <input type="hidden" name="amount" value="2.95">
                <input type="hidden" name="no_shipping" value="1">
                <input type="hidden" name="return" value="http://localhost:13769">
                <input type="hidden" name="notify_url" value="https://localhost:13769/Home/Ipn">
                <button class="btn btn-primary submit-button" type="submit">Pay with PayPal</button>
            </fieldset>

        </form>
    </div>

El control de HomeControler / Ipn Action es el siguiente

public ActionResult Ipn()
{
    // Receive IPN request from PayPal and parse all the variables returned
    var formVals = new Dictionary<string, string>();

    formVals.Add("cmd", "_notify-validate");

    // if you want to use the PayPal sandbox change this from false to true
    string response = GetPayPalResponse(formVals, false);

    if (response == "VERIFIED")
    {
        string transactionID = Request["txn_id"];
        string sAmountPaid = Request["mc_gross"];
        string deviceID = Request["custom"];

        //validate the order
        Decimal amountPaid = 0;
        Decimal.TryParse(sAmountPaid, out amountPaid);

        if (sAmountPaid == "2.95")
        {
            // take the information returned and store this into a subscription table
            // this is where you would update your database with the details of the tran

            return View();

        }
        else
        {
            // let fail - this is the IPN so there is no viewer
            // you may want to log something here
        }
    }

    return View();
}

Mi pregunta es incluso después de que se haya realizado el pago, por encima del método de acción Ipn no se está activando. No puedo hacer una depuración. ¿Cómo puedo hacer eso?