how to integrate paypal IPN using php example

Receiving Your First Notification

To process a sample IPN message, build a listener and host it on your web server. Once the listener is up and running, test it by using the PayPal Sandbox to send a simulated IPN message to the listener.

The steps below include PHP snippets that show how to code a simple IPN listener.

1. Upon receipt of a notification from PayPal, send an empty HTTP 200 response.

   <?php
   
      // Send an empty HTTP 200 OK response to acknowledge receipt of the notification 
      header('HTTP/1.1 200 OK'); 
     

2. Extract variables from the notification for later processing.
   
   Note that how you process a particular notification depends on its type. For example, if a notification applies to a completed payment, you could extract these variables from the message:

     // Assign payment notification values to local variables
     $item_name        = $_POST['item_name'];
     $item_number      = $_POST['item_number'];
     $payment_status   = $_POST['payment_status'];
     $payment_amount   = $_POST['mc_gross'];
     $payment_currency = $_POST['mc_currency'];
     $txn_id           = $_POST['txn_id'];
     $receiver_email   = $_POST['receiver_email'];
     $payer_email      = $_POST['payer_email'];
     

3. Use the notification to build the acknowledgement message required by the IPN authentication protocol.
   

     // Build the required acknowledgement message out of the notification just received
     $req = 'cmd=_notify-validate';               // Add 'cmd=_notify-validate' to beginning of the acknowledgement
   
     foreach ($_POST as $key => $value) {         // Loop through the notification NV pairs
       $value = urlencode(stripslashes($value));  // Encode these values
       $req  .= "&$key=$value";                   // Add the NV pairs to the acknowledgement
     }

4. Post the acknowledgement back to PayPal, so PayPal can determine whether the original notification was tampered with.
   

     // Set up the acknowledgement request headers
     $header  = "POST /cgi-bin/webscr HTTP/1.1\r\n";                    // HTTP POST request
     $header .= "Content-Type: application/x-www-form-urlencoded\r\n";
     $header .= "Content-Length: " . strlen($req) . "\r\n\r\n";
   
     // Open a socket for the acknowledgement request
     $fp = fsockopen('ssl://www.sandbox.paypal.com', 443, $errno, $errstr, 30);
   
     // Send the HTTP POST request back to PayPal for validation
     fputs($fp, $header . $req);

5. Parse PayPal's response to your acknowledgement to determine whether the original notification was OK - if so, process it.

     while (!feof($fp)) {                     // While not EOF
       $res = fgets($fp, 1024);               // Get the acknowledgement response
       if (strcmp ($res, "VERIFIED") == 0) {  // Response contains VERIFIED - process notification
   
         // Send an email announcing the IPN message is VERIFIED
         $mail_From    = "IPN@example.com";
         $mail_To      = "Your-eMail-Address";
         $mail_Subject = "VERIFIED IPN";
         $mail_Body    = $req;
         mail($mail_To, $mail_Subject, $mail_Body, $mail_From);
   
         // Authentication protocol is complete - OK to process notification contents
   
         // Possible processing steps for a payment include the following:
   
         // Check that 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
   
       } 
       else if (strcmp ($res, "INVALID") == 0) { Response contains INVALID - reject notification
   
         // Authentication protocol is complete - begin error handling
   
         // Send an email announcing the IPN message is INVALID
         $mail_From    = "IPN@example.com";
         $mail_To      = "Your-eMail-Address";
         $mail_Subject = "INVALID IPN";
         $mail_Body    = $req;
   
         mail($mail_To, $mail_Subject, $mail_Body, $mail_From);
       }
     }

6. Close the file and end the PHP script.
   
   

     fclose($fp);  // Close the file