// read the post from PayPal system and add 'cmd'
$req = 'cmd=_notify-synch';

$tx_token = $_GET['tx'];
$payer_email;
$receiver_email;
$item_number;
$auth_token = "i6QuA8_x0tzxn1EGSCSZQzvrVQvm0DjwF6JJcLBis0PcPxS81srjQBKR3wW";
$req .= "&tx=$tx_token&at=$auth_token";

// post back to PayPal system to validate
$header .= "POST /cgi-bin/webscr HTTP/1.0\r\n";
$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
$header .= "Content-Length: " . strlen($req) . "\r\n\r\n";
$fp = fsockopen ('www.paypal.com', 80, $errno, $errstr, 30);

if (!$fp) {
   echo "HTTP ERROR";
}
else {
 fputs ($fp, $header . $req);
 $res = '';
 $headerdone = false;
 while (!feof($fp)) {
     $line = fgets ($fp, 1024); 
  if (strcmp($line, "\r\n") == 0) {
     $headerdone = true;
  }
  else if ($headerdone)
  {
     $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);
  }
  $payer_email = $keyarray['payer_email'];//付款人帐号
  $receiver_email = $keyarray['receiver_email'];//收款帐号
$item_number = $keyarray['item_number'];//名称
....还有很多可以参考文档


se if (strcmp ($lines[0], "FAIL") == 0) {
     echo "log for manual investigation";
 }

}

fclose ($fp);