Paypal-传递多个'；自定义'；变量

我的网站链接到Paypal。在我的网站上，我将信息传递给PayPal，如下所示；

<form target="paypal" action="https://www.sandbox.paypal.com/cgi-bin/webscr" method="post">
        <input type="hidden" name="cmd" value="_cart">
        <input type="hidden" name="business" value="youremail@email.com">
        <input type="hidden" name="currency_code" value="EUR">
        <input type="hidden" name="upload" value="1">
        <input type="hidden" name="custom" value="<?php echo $randomString ?>"/>
        <input type="hidden" name="return" value="http://www.example.com/thank-you/">
        <input type="hidden" name="rm" value="2"> 
        <?php 
        if (($Adults > 0) && ($Students > 0) && ($Children > 0))
        {
            echo "<input type='hidden' name='item_name_1' value='" . $selectroute ." (Adult - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_1' value='15'>";
            echo "<input type='hidden' name='quantity_1' value='" . $Adults . "'>";
            echo "<input type='hidden' name='item_name_2' value='" . $selectroute ." (Student - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_2' value='15'>";
            echo "<input type='hidden' name='quantity_2' value='" . $Students . "'>";
            echo "<input type='hidden' name='item_name_3' value='" . $selectroute ." (Child - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_3' value='15'>";
            echo "<input type='hidden' name='quantity_3' value='" . $Children . "'>";
        }
        elseif (($Adults > 0) && ($Students > 0))
        {
            echo "<input type='hidden' name='item_name_1' value='" . $selectroute ." (Adult - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_1' value='15'>";
            echo "<input type='hidden' name='quantity_1' value='" . $Adults . "'>";
            echo "<input type='hidden' name='item_name_2' value='" . $selectroute ." (Student - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_2' value='15'>";
            echo "<input type='hidden' name='quantity_2' value='" . $Students . "'>";
        }
        elseif (($Students > 0) && ($Children > 0))
        {
            echo "<input type='hidden' name='item_name_1' value='" . $selectroute ." (Student - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_1' value='15'>";
            echo "<input type='hidden' name='quantity_1' value='" . $Students . "'>";
            echo "<input type='hidden' name='item_name_2' value='" . $selectroute ." (Child - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_2' value='15'>";
            echo "<input type='hidden' name='quantity_2' value='" . $Children . "'>";
        }
        elseif (($Adults > 0) && ($Children > 0))
        {
            echo "<input type='hidden' name='item_name_1' value='" . $selectroute ." (Adult - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_1' value='15'>";
            echo "<input type='hidden' name='quantity_1' value='" . $Adults . "'>";
            echo "<input type='hidden' name='item_name_2' value='" . $selectroute ." (Child - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_2' value='15'>";
            echo "<input type='hidden' name='quantity_2' value='" . $Children . "'>";
        }
        elseif ($Adults > 0)
        {
            echo "<input type='hidden' name='item_name_1' value='" . $selectroute ." (Adult - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_1' value='15'>";
            echo "<input type='hidden' name='quantity_1' value='" . $Adults . "'>";
        }
        elseif ($Students > 0)
        {
            echo "<input type='hidden' name='item_name_1' value='" . $selectroute ." (Student - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_1' value='15'>";
            echo "<input type='hidden' name='quantity_1' value='" . $Students . "'>";
        }
        elseif ($Children > 0)
        {
            echo "<input type='hidden' name='item_name_1' value='" . $selectroute ." (Child - " . $ticket .")'>";
            echo "<input type='hidden' name='amount_1' value='15'>";
            echo "<input type='hidden' name='quantity_1' value='" . $Children . "'>";
        }
        ?>
        <input type="image" src="https://www.paypalobjects.com/webstatic/en_US/btn/btn_paynow_cc_144x47.png" border="0" name="submit" alt="PayPal - The safer, easier way to pay online!" style="position:relative; top: 8em; padding-left:45em;">
        <img alt="" border="0" src="https://www.sandbox.paypal.com/en_US/i/scr/pixel.gif" width="1" height="1">
    </form>

付款后，用户会被重定向回我网站上的"谢谢"页面。在这个页面上，我可以在确认电子邮件中使用通过PayPal传递的信息。

        $ItemName1 = $keyarray['item_name1'];
        $ItemName2 = $keyarray['item_name2'];
        $ItemName3 = $keyarray['item_name3'];
        $TotalCost = $keyarray['mc_gross'];
        $Quantity1 = $keyarray['quantity1'];
        $Quantity2 = $keyarray['quantity2'];
        $Quantity3 = $keyarray['quantity3'];
        $ItemCost1 = $keyarray['mc_gross_1'];
        $ItemCost2 = $keyarray['mc_gross_2'];
        $ItemCost3 = $keyarray['mc_gross_3'];
        $Currency = $keyarray['mc_currency'];
        $BookingReference = $keyarray['custom'];
        $FirstName = $keyarray['first_name'];
        $LastName = $keyarray['last_name'];
        $Email = $keyarray['payer_email'];

我已经使用了自定义变量，我相信我只能使用一次——这是正确的吗？但我需要再传递两个变量，包括出发时间和返回时间-如果我不能再次使用自定义变量，我该如何传递这些变量？