paypal沙盒表单不起作用，连接超时错误

Question

我使用beiow表单使用PayPal付款。

<?php
$url = "https://www.sandbox.paypal.com/cgi-bin/webscr";
$price=90.00;
//$url = "https://www.paypal.com/cgi-bin/webscr";
?>
<form action="<?=$url?>" method="post" style="padding: 0; margin: 0;">
    <input type="hidden" name="cmd" value="_xclick" />
    <input type="hidden" name="business" value="xyz@gmail.com" />
    <input type="hidden" name="quantity" value="1" />
    <input type="hidden" name="item_name" value="full licence" />
    <input type="hidden" name="item_number" value="1" />
    <input type="hidden" name="amount" value="<?=$price?>" />
    <input type="hidden" name="shipping" value="0" />
    <input type="hidden" name="no_note" value="1" />
    <input type="hidden" name="notify_url" value="http://www.example.com/ipn.php">
    <input type="hidden" name="return" value="http://www.example.com/dev/login/success.php">
    <input type="hidden" name="cancel_return" value="http://www.example.com/dev/login/paypal_cancel.php">
    <input type="hidden" name="currency_code" value="GBP" />
    <input type="hidden" name="rm" value="2" >
    <input type="image" border="0" name="paypal" src="images/btn_paypal_nl.gif" onClick=""/>
</form>

如果我将$url更改为真实帐户，那么一切正常。但是如果我使用沙盒URL，那么浏览器会占用太多时间，最后会返回The connection has timed out错误。