在PAYPAL递归事务中没有返回自定义参数

Question

我将以用户订阅的形式实现paypal ... 贝娄码运行良好...... 交易也很好......

但是我没有收到我发送的'custom parameters'（如下面的表格代码所示）......

<form name="_xclick" id="_xclick" action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
 <!-- Identify your business so that you can collect the payments. -->
    <input type="hidden" name="business" value="xxx@xxx.com">
 <!-- Specify a Subscribe button. -->
    <input type="hidden" name="cmd" value="_xclick-subscriptions">
    <!-- Identify the subscription. -->
    <input type="hidden" name="item_name" value="<?php echo $description; ?>">
    <!-- Set the terms of the regular subscription. -->
    <input type="hidden" name="currency_code" value="USD">
    <input type="hidden" name="a3" value="<?php echo $amount; ?>">
    <input type="hidden" name="p3" value="1">
    <input type="hidden" name="t3" value="<?php echo $trial_period; ?>">
    <!-- Set recurring payments until canceled. -->
    <input type="hidden" name="src" value="1">

        <input type="hidden" name="no_shipping" value="1">
      <input type="hidden" name="notify_url" value="<?php echo $return_domain;?>">
      <input type="hidden" name="cancel_return" value="<?php echo $cancel_return;?>">
      <input type="hidden" name="return" id="return" value="<?php echo $return_domain;?>" />
      <input type="hidden" name="custom" value="<?php echo $serialized_cust_par;?>" />
     </form>