Paypal auto return button doesn't override default url

I have enabled automatic refunds after a PayPal customer purchase in the PayPal sandbox settings. I have also specified the return url in settings eg. www.example.com

because it was necessary. However, I want the returned url to be dynamically set in the payment button for example.

<form name="_xclick" action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
    <input type="hidden" name="cmd" value="_xclick">
    <input type="hidden" name="business" value="company@life.com">
    <input type="hidden" name="currency_code" value="GBP">
    <input type="hidden" name="item_name" value="Enquiry Estimate">
    <input type="hidden" name="amount" value="250">
    <input type="hidden" name="return" value="http://example.com/order/success?order=1654321">
    <input type="hidden" name="notify_url" value="">
    <input type="submit" value="Accept and Pay Now" />
</form>

      

        
        
        
      

    

The autorepeatable url when a user pays with that specific button should be

http://example.com/order/success?order=1654321

      

        
        
        
      

    

instead example.com

Why is the URL not being redefined? Whenever a payment is made, Paypal is only redirected to example.com

.