Php 贝宝定期支付代码集成

我是贝宝整合的新手。我需要每月贝宝用户定期付款。我已使用此方法进行即时付款：

<form method="post" action="https://www.paypal.com/cgi-bin/webscr" name="form_paypal" id="paypal_form">
    <input type="hidden" name="amount"  value="<?php echo $amount; ?>" />
    <input type="hidden" name="cmd" value="_xclick" /> 
    <input type="hidden" name="no_note" value="1" />
    <input type="hidden" name="lc" value="USA" />
    <input type="hidden" name="currency_code" value="USD" />
    <input type="hidden" name="business" value="test@gmail.com">
    <input type="hidden" name="custom" value='<?php echo $custom;?>' />
    <input type="hidden" name="first_name" value= "Anonymous"  />
    <input type="hidden" name="last_name" value="User"  />
    <input type="hidden" name="payer_email" value="customer@example.com"  />
    <input type="hidden" name="item_number" value="123" / >
    <input type="hidden" name="item_name" value="test.co Services" / >
    <input type="hidden" name="notify_url" value="http://test.co/pg_return.php" / >
    <input type="submit" value="Pay" name="pay" id="paypal_submit">
</form>

根据您的示例，以下是如何使用相同的方法设置订阅/定期付款：

<form method="post" action="https://www.paypal.com/cgi-bin/webscr" name="form_paypal" id="paypal_form">
    <input type="hidden" name="cmd" value="_xclick-subscriptions" /> 
    <input type="hidden" name="business" value="test@gmail.com">
    <input type="hidden" name="a3"  value="<?php echo $amount; ?>" />
    <input type="hidden" name="t3" value="M" >
    <input type="hidden" name="p3" value="1" >
    <input type="hidden" name="src" value="1" >
    <input type="hidden" name="no_note" value="1" />
    <input type="hidden" name="lc" value="US" />
    <input type="hidden" name="currency_code" value="USD" />
    <input type="hidden" name="custom" value="<?php echo $custom;?>"/>
    <input type="hidden" name="first_name" value= "Anonymous"  />
    <input type="hidden" name="last_name" value="User"  />
    <input type="hidden" name="item_number" value="123" / >
    <input type="hidden" name="item_name" value="test.co Services" / >
    <input type="hidden" name="notify_url" value="http://test.co/pg_return.php" / >
    <input type="submit" value="Pay" name="pay" id="paypal_submit">
</form>


如果我想使用此表单订阅多个产品，该怎么办？