PayPal auto return cannot grab params - php

Question

PayPal documentation is make my head spinning!
I has copied sample from somewhere to setup auto return upon payment completion, I created a page called success.php to grab returned params, somehow I was not success to display those returned params, can anyone expert in Paypal please help to check what's wrong with below code?
success.php
<?php
$req = 'cmd=_notify-synch';
$tx_token = $_GET['tx'];
$auth_token = "ZgTzjTg49XZGeD54WsS";
$req .= "&tx=".$tx_token."&at=".$auth_token;
foreach($_POST as $key => $value){
$value = urlencode(stripslashes($value));
$req .= '&'.$key.'='.$value;
}
$header = "POST /cgi-bin/webscr HTTP/1.0\r\n";
$header .= "Host: http://www.sandbox.paypal.com\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: ".strlen($req)."\r\n\r\n";
// url for paypal sandbox
$fp = fsockopen ('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30);
if(!$fp){
// HTTP ERROR
}else{
fputs($fp, $header . $req);
// read the body data
$res = '';
$headerdone = false;
while(!feof($fp)){
$line = fgets ($fp, 1024);
if(strcmp($line, '\r\n') == 0){
// read the header
$headerdone = true;
}else if($headerdone){
// header has been read. now read the contents
$res .= $line;
}
}
// parse the data
$lines = explode('\n', $res);
$keyarray = array();
if(strcmp($lines[0], 'SUCCESS') == 0){
for($i=1; $i<count($lines);$i++){
list($key,$val) = explode('=', $lines[$i]);
$keyarray[urldecode($key)] = urldecode($val);
}
// check the payment_status is Completed
// check that txn_id has not been previously processed
// check that receiver_email is your Primary PayPal email
// check that payment_amount/payment_currency are correct
// process payment
$firstname = $keyarray['first_name'];
$lastname = $keyarray['last_name'];
$itemname = $keyarray['item_name'];
$amount = $keyarray['payment_gross'];
echo '<p><h3>Thank you for your purchase!</h3></p>';
echo '<b>Payment Details</b><br>';
echo '<ul>';
echo '<li>Name: '.$firstname.' '.$lastname.'</li>';
echo '<li>Item: '.$itemname.'</li>';
echo '<li>Amount: '.$amount.'</li>';
echo '</ul>';
}else if(strcmp($lines[0], 'FAIL') == 0){
// log for manual investigation
}
}
fclose($fp);
?>
Your transaction has been completed, and a receipt for your purchase has been emailed to you.<br>
This is auto returned URL:
http://sitename.com/success.php?tx=88L2235578117773M&st=Completed&amt=318.00&cc=USD&cm=2013-23&item_number=&sig=HzS1ku7OeDrZJVZcXta6X9jrf71vct7Spstv0%2bW7lxj%2bqRtQXBDO9pqs%2bhmzaoSGs6EDjpEFCnPwOGYzlZ1FMbyw%2fIpF6%2bVMFCNDBYuLdFTYkWaiwG70IpyEMGFFNh1aJUsn3W%2fQK6ad6HOC7%2fzccQPUebhMSqp4WBw%2bRw%2f4tw4%3d

Answer 1

I find that using the Sandbox is not very good for final testing, so once you have established that you code is working, it is best to go live and then test with $1 transactions.
Also, you won't get all of your customer's order details returned, so it is better to simply retrieve the order number and populate your receipt from a database record that was created prior to sending details to Paypal.
The data to retrieve for your invoice number will be found as Request("item_number")