PayPal操作不起作用

    <p>
     <form action="//www.paypal.com/cgi-bin/webscr" method="post">
        <input type="hidden" name="cmd" value="_cart">
        <input type="hidden" name="upload" value="1" />
        <input type="hidden" name="business" value="alex@phpacademy.org">
        <?php paypal_items();?>
        <input type="hidden" name="currency_code" value="INR">
        <input type="hidden" name="amount" value="<?php echo $total;?>">
        <input type="image" src="http://www.paypal.com/en_US/i/btn/x-click-but03.gif" name="submit" alt="Make payments with PayPal - it's fast, free and secure!">
        </form>

使用此编码不起作用。.那我该怎么办？