Paypal IPN response on specific port

Question

I'm integrating Paypal with CakePHP 3.x. but I'm facing problem to get IPN response from PayPal. my site is running on port number 4902.

My form is

<form method="post" accept-charset="utf-8" action="https://www.sandbox.paypal.com/cgi-bin/webscr">
    <div style="display:none;">
     <input type="hidden" name="_method" value="POST">
    </div>
    <input type="hidden" name="business" value="mypaypalemail@domain.com">
       <input type="hidden" name="cmd" value="_xclick">
    <input type="hidden" name="item_name" value="Test Item">
    <input type="hidden" name="amount" value="18">
    <input type="hidden" name="cpp_header_image" value="http://example.com/images/logo.jpg">
    <input type="hidden" name="no_shipping" value="2">
    <input type="hidden" name="shipping" value="4.99">
    <input type="hidden" name="currency_code" value="USD">
    <input type="hidden" name="quantity" id="quantity" value="1">
    <input type="hidden" name="handling" value="0">
    <input type="hidden" name="custom" value="21">
    <input type="hidden" name="cancel_return" value="http://example.com:4902/payments/cancel">
    <input type="hidden" name="notify_url" value="http://example.com:4902/payments/ipn">
    <input type="hidden" name="return" value="http://example:4902/payments/success">
    <div class="submit">
    <input type="submit" class="button greenbtn" value="Pay Now">
    </div>
   </form>

It is working fine if I run this code without any port number. but if I use port number then I get success and cancel response from PayPal but not get IPN response, I had tried with Paypal IPN Simulator, it says me that We're sorry, URL with port number is not allowed for IPN.

And I can't use any other port. can anyone help me please to resolve this issue?

---Edited-----

Like PayPal IPN on a port other than 80 I am not using Nginx server

Thanks.