PayPal response not coming in PHP - php

Question

I am create my sandbox account for testing. I can perform payment successful but and I am also redirect to my success page but I cannot get TX parameter when success page is loaded.
I am pass return url in my form and I am also setting return URL in my PayPal account and also turn Payment Data Transfer, but I cannot get any parameter when success page is loaded.
BUY.PHP
<?php
$paypal_url='https://www.sandbox.paypal.com/cgi-bin/webscr'; // Test Paypal API URL
$paypal_id='my-id-facilitator#gmail.com'; // Business email ID
?>
<form action='https://www.sandbox.paypal.com/cgi-bin/webscr' method='post' name='form1'>
<input type='hidden' name='business' value='Demo for paypal'>
<input type='hidden' name='cmd' value='_xclick'>
<input type='hidden' name='item_name' value='demo'>
<input type='hidden' name='item_number' value='1'>
<input type='hidden' name='amount' value='1'>
<input type='hidden' name='rm' value='1'>
<input type='hidden' name='no_shipping' value='1'>
<input type='hidden' name='currency_code' value='USD'>
<input type='hidden' name='cancel_return' value='http://my-site.com/cancel.php'>
<input type='hidden' name='return' value='http://my-site.com/success.php'>
<input type="image" src="https://paypal.com/en_US/i/btn/btn_buynowCC_LG.gif" name="submit">
</form>
SUCCESS.PHP
<?php
$item_transaction = $_GET['tx']; // Paypal transaction ID
$item_price = $_GET['amt']; // Paypal received amount
$item_currency = $_GET['cc']; // Paypal received currency type
echo $item_transaction;
echo "<br>".$item_price;
echo "<br>".$item_currency;
?>