How to add callback url for paypal button?

Question

API

There is a paypal button on the site.
Button code:

<form action="https://www.paypal.com/cgi-bin/webscr" method="post" target="_top">
            <input type="hidden" name="cmd" value="_xclick">
            <input type="hidden" name="business" value="...">
            <input type="hidden" name="lc" value="IE">
            <input type="hidden" name="button_subtype" value="services">
            <input type="hidden" name="no_note" value="0">
            <input type="hidden" name="cn" value="Add special instructions to the seller:">
            <input type="hidden" name="no_shipping" value="2">
            <input type="hidden" name="currency_code" value="EUR">
            <input type="hidden" name="bn" value="PP-BuyNowBF:btn_buynowCC_LG.gif:NonHosted">
            <table>
                <tr><td><input type="hidden" name="on0" value="subscription options in EUR"><span style="color:white" > subscription options in EUR</span></td></tr><tr><td><select name="os0">
                    <option id="opte0" value="1 month">1 month &euro;110.00 EUR</option>
                    <option id="opte1" value="3 month">3 month &euro;315.00 EUR</option>
                    <option id="opte2" value="6 month">6 month &euro;600.00 EUR</option>
                    <option id="opte3" value="12 month">12 month &euro;1,020.00 EUR</option>
                </select> </td></tr>
            </table>
            <input type="hidden" name="option_select0" value="1 month">
            <input id="opte0_amount"   type="hidden" name="option_amount0" value="110.00">
            <input type="hidden" name="option_select1" value="3 month">
            <input id="opte1_amount"  type="hidden" name="option_amount1" value="315.00">
            <input type="hidden" name="option_select2" value="6 month">
            <input id="opte2_amount"  type="hidden" name="option_amount2" value="600.00">
            <input type="hidden" name="option_select3" value="12 month">
            <input id="opte3_amount" type="hidden" name="option_amount3" value="1020.00">
            <input type="hidden" name="option_index" value="0">
            

            <input type="image" src="https://www.paypalobjects.com/en_US/i/btn/btn_buynowCC_LG.gif" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!">
            <img alt="" border="0" src="https://www.paypalobjects.com/en_US/i/scr/pixel.gif" width="1" height="1">
        </form>

How to add callback url? It is necessary that information about payment would come to the server. I can't figure out where and how to add the path for the callback