too long

I've used paypal express checkout sandbox, but When I click to purchase something, doesn't show any price or item name in paypal.

On my page I've put this form :

<form action='expresscheckout.php' METHOD='POST'>
<input type='image' name='submit' src='https://www.paypal.com/en_US/i/btn/btn_xpressCheckout.gif' border='0' align='top' alt='Check out with PayPal'/>
</form>

And I've included these two codes from paypal into my scripts:

https://www.paypal-labs.com/integrationwizard/ecpaypal/download.php?file=ecfile

https://www.paypal-labs.com/integrationwizard/ecpaypal/download.php?file=pplibfile

As I said, when I click on pay button , it takes me to the paypal sandbox, but with no price or item name. I even tried this with real API name and pass but still no price.

Meanwhile, I've also manually set the price in the expressscheckout.php :

$paymentAmount = $_SESSION["Payment_Amount"];

to

$paymentAmount = 32;

For Website Payments Standard : I have put following two tags in my form tag :

<input type="hidden" name="item_name" value="<?php print $itemName; ?> "/>
<input type="hidden" id="amount" name="amount" value="<?php print $amount; ?>"/>