Paypal IPN option_selection变量JCart的问题

Question

The paypal IPN option_selection variable does not work in my PHP generated url. I'm generating the URL through the gateway.php page of Jcart. My goal is to add extra details like color and size for each user's selection in my paypal cart. My name, quantity, price, and shipping IPN variables work fine and all display in my paypal cart with the PHP code below. I've tried isolating the issue by changing the value given in option_selection but no matter what I try the option_selection value does not appear in my paypal cart. Is option_selection the right IPN variable to use? And if so what am I doing wrong here?

PHP CODE:

        foreach ($jcart->get_contents() as $item) {


        $queryString .= '&item_name_' . $count . '=' . urlencode(parsecolor($item['name']));
        $queryString .= '&amount_' . $count . '=' . urlencode($item['price']);
        $queryString .= '&quantity_' . $count . '=' . urlencode($item['qty']);
        $queryString .= '&option_selection1_' . $count . '=' . urlencode($item['name']);
  $queryString .= '&shipping_' . $count . '=' . "6.00";

        // Increment the counter
        ++$count;
    }

Generated string w/out merchant ID

?cmd=_cart&upload=1&charset=utf-8&currency_code=USD&return=&notify_url=&item_name_1=Green+Straps&amount_1=40&quantity_1=1&option_selection1_1=Green25