// เช็คข้อมูลการชำระเงินจาก email 
	// ipn message จากระบบของ paypal
	public function callback(){				
		// read the IPN msg from PayPal and add 'cmd' for your verification request
		$req = 'cmd=_notify-validate';
		
		// append the IPN msg, in NVP format, to your verification request
		foreach ($_POST as $key => $value) {
			$value = urlencode(stripslashes($value));
			$req .= "&$key=$value";
		}
		
		// set up the headers for your verification request
		// POST your verification requests to PayPal (here, the Sandbox)
		$header  = "POST /cgi-bin/webscr HTTP/1.0\r\n";
		$header .= "Host: www.sandbox.paypal.com:443\r\n";
		
		// $header .= "Host: ipnpb.paypal.com:443\r\n";      // endpoint for Live apps
		
		$header .= "Content-Type: application/x-www-form-urlencoded\r\n";
		$header .= "Content-Length: " . strlen($req) . "\r\n\r\n";
		
		// open the socket
		$fp = fsockopen ('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30);
		
		// for live applications, use:
		// $fp = fsockopen ('ssl://ipnpb.paypal.com', 443, $errno, $errstr, 30);
		
		$ipn_response = '';
		if (!$fp) {
			// HTTP error
			echo "HTTP socket error! Unable to open URL";
		} else {
			// POST verification request
			fputs ($fp, $header . $req);
			while(!feof($fp)) { 
				$ipn_response .= fgets($fp, 1024); 
			}
			
			if( preg_match("/VERIFIED/", $ipn_response) ){
				$msg = "ok";
				$custom = isset($_POST['custom']) ? $_POST['custom'] : '';
				// ยืนยันออเดอร์ ชำระเงินผ่านทาง paypal 
				// $this->order_model->confirm_order( $order_id );
			}else{
				$msg = "not ok";
			}
		}
	}