how to specify notify url and return url in refund post request in Paypal

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.NET

PayPal

I am using refund API of Paypal. It is going well but it does not call my INP and neither it gets return to my site.
My code is as follows:

"<form id='paymentForm' action='https://api-3t.sandbox.paypal.com/nvp' method='post'>" +
           "<input type='hidden' name='USER' value='XXXX'>" +
           "<input type='hidden' name='PWD' value='XXXX'>" +
           "<input type='hidden' name='SIGNATURE' value='XXXX'>" +
           "<input type='hidden' name='notify_url' value='http://59.90.163.122:4321/CommonMenus/IPN.aspx'>"+
           "<input type='hidden' name='RETURN' value='http://59.90.163.122:4321/CommonMenus/ThankYou.aspx'>" +
           "<input type='hidden' name='TRANSACTIONID' value='XXXX'>" +
           "<input type='hidden' name='METHOD' value='RefundTransaction'>" +
           "<input type='hidden' name='VERSION' value='94'>" +
           "<input type='hidden' name='REFUNDTYPE' value='Partial'>" +
           "<input type='hidden' name='AMT' value='25'>" +
           "<input type='hidden' name='CURRENCYCODE' value='USD'>" +
    "</form>";

I have specified both notify_url and return. But it neither notify nor return. Same urls are working for Payment API but not understanding issue with refund