Webhooks

APICurrentLast updated: March 15th 2022, @ 1:14:38 pm


PayPal REST APIs use webhooks for event notifications. Webhooks are push API calls that let your app know an event has happened.

How to use

Configure a webhook listener for your app and then create a webhook and subscribe it to the transaction events that you need.

Tip: You can verify your listener is working by using our webhooks simulator.

Messages

Each JSON-formatted POST notification message contains event information based on the resource type and the event type. For example, an event that let your app know an authorization for payment occured would be of resource type authorization and an event type of created.

When your app receives a notification message, it must:

  • Verify that the notification message came from PayPal
  • Was not altered or corrupted during transmission
  • Was targeted for you
  • Contains a valid signature
  • Respond with an HTTP 200 code

Note: If your app responds with any other status code, PayPal tries to resend the notification message 25 times over the course of three days.

Message signature

Because anyone could, theoretically, send a POST to your app's listener, we sign our notification messages and send them over HTTPS (SSL/TLS). Event headers for notification messages contain the PayPal-generated asymmetric signature and information that you can use to validate the signature.

Event header generation

To generate the signature, PayPal concatenates and separates these items with the pipe (|) character.

Event headerDescription
PAYPAL-TRANSMISSION-SIGThe PayPal-generated asymmetric signature.
PAYPAL-AUTH-ALGOThe algorithm that PayPal used to generate the signature and that you can use to verify the signature.
PAYPAL-CERT-URLThe X509 public key certificate.
Download the certificate from this URL and use it to verify the signature.

The authentication algorithm specified in PAYPAL-AUTH-ALGO uses an asymmetric signature algorithm, such as RSA with SHA256. This enables PayPal to use a private key to create the signature in PAYPAL-TRANSMISSION-SIG and enables you to use a public key defined in PAYPAL-CERT-URL to verify the webhook.

Event header validation

To validate a signature, use this input string:

<transmissionId>|<timeStamp>|<webhookId>|<crc32>

The fields in the string are:

FieldDescription
transmissionIdThe unique ID of the HTTP transmission from the PAYPAL-TRANSMISSION-ID header.
timeStampThe date and time when the HTTP message was transmitted from the PAYPAL-TRANSMISSION-TIME header.
webhookIdThe ID of the webhook resource for the destination URL to which PayPal delivers the event notification.
crc32The Cyclic Redundancy Check (CRC32) checksum for the body of the HTTP payload.

Note: When you validate the signature for notification messages that the Webhooks simulator generates, the webhook ID might vary depending on which method you used to simulate the event:

  • If you used a webhook ID, use that same ID to validate the event.
  • If you used a webhook URL, use WEBHOOK_ID to validate the event.

This Java pseudocode combines all headers and the input string to complete the verification:

// #Validate Webhook Sample
//
// This sample code demonstrates how to validate a webhook received on your
// web server. This sample assumes that you use the java servlet, which returns
// the HttpServletRequest object. However, you can modify this code to
// your specific case.
//
package com.paypal.api.payments.servlet;
import com.paypal.api.payments.CreditCard;
import com.paypal.api.payments.Event;
import com.paypal.api.payments.util.ResultPrinter;
import com.paypal.base.Constants;
import com.paypal.base.rest.APIContext;
import com.paypal.base.rest.PayPalRESTException;
import org.apache.log4j.Logger;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;
import java.security.SignatureException;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Map;
import static com.paypal.api.payments.util.SampleConstants.*;
public class ValidateWebhookServlet extends HttpServlet {
  private static final long serialVersionUID = 1 L;
  private static final Logger LOGGER = Logger.getLogger(ValidateWebhookServlet.class);
  public static final String WebhookId = "4JH86294D6297924G";
  @Override
  protected void doGet(HttpServletRequest req, HttpServletResponse resp)
  throws ServletException, IOException {
    doPost(req, resp);
  }
  // ##Validate Webhook
  @Override
  protected void doPost(HttpServletRequest req, HttpServletResponse resp)
  throws ServletException, IOException {
    try {
      // ### Api Context
      APIContext apiContext = new APIContext(clientID, clientSecret, mode);
      // Set the webhookId that you received when you created this webhook.
      apiContext.addConfiguration(Constants.PAYPAL_WEBHOOK_ID, WebhookId);
      Boolean result = Event.validateReceivedEvent(apiContext, getHeadersInfo(
        req), getBody(req));
      System.out.println("Result is " + result);
      LOGGER.info("Webhook Validated:  " + result);
      ResultPrinter.addResult(req, resp, "Webhook Validated:  ", CreditCard.getLastRequest(),
        CreditCard.getLastResponse(), null);
    } catch (PayPalRESTException e) {
      LOGGER.error(e.getMessage());
      ResultPrinter.addResult(req, resp, "Webhook Validated:  ", CreditCard.getLastRequest(),
        null, e.getMessage());
    } catch (InvalidKeyException e) {
      LOGGER.error(e.getMessage());
      ResultPrinter.addResult(req, resp, "Webhook Validated:  ", CreditCard.getLastRequest(),
        null, e.getMessage());
    } catch (NoSuchAlgorithmException e) {
      LOGGER.error(e.getMessage());
      ResultPrinter.addResult(req, resp, "Webhook Validated:  ", CreditCard.getLastRequest(),
        null, e.getMessage());
    } catch (SignatureException e) {
      LOGGER.error(e.getMessage());
      ResultPrinter.addResult(req, resp, "Webhook Validated:  ", CreditCard.getLastRequest(),
        null, e.getMessage());
    }
  }
  // Simple helper method to help you extract the headers from HttpServletRequest object.
  private static Map < String, String > getHeadersInfo(HttpServletRequest request) {
    Map < String, String > map = new HashMap < String, String > ();
    @SuppressWarnings("rawtypes")
    Enumeration headerNames = request.getHeaderNames();
    while (headerNames.hasMoreElements()) {
      String key = (String) headerNames.nextElement();
      String value = request.getHeader(key);
      map.put(key, value);
    }
    return map;
  }
  // Simple helper method to fetch request data as a string from HttpServletRequest object.
  private static String getBody(HttpServletRequest request) throws IOException {
    String body;
    StringBuilder stringBuilder = new StringBuilder();
    BufferedReader bufferedReader = null;
    try {
      InputStream inputStream = request.getInputStream();
      if (inputStream != null) {
        bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
        char[] charBuffer = new char[128];
        int bytesRead = -1;
        while ((bytesRead = bufferedReader.read(charBuffer)) > 0) {
          stringBuilder.append(charBuffer, 0, bytesRead);
        }
      } else {
        stringBuilder.append("");
      }
    } catch (IOException ex) {
      throw ex;
    } finally {
      if (bufferedReader != null) {
        try {
          bufferedReader.close();
        } catch (IOException ex) {
          throw ex;
        }
      }
    }
    body = stringBuilder.toString();
    return body;
  }
}

Sample message payload

The sample here is a notification that let your app know an authorization for payment occurred.

{
  "id": "8PT597110X687430LKGECATA",
  "create_time": "2013-06-25T21:41:28Z",
  "resource_type": "authorization",
  "event_type": "PAYMENT.AUTHORIZATION.CREATED",
  "summary": "A payment authorization was created",
  "resource": {
    "id": "2DC87612EK520411B",
    "create_time": "2013-06-25T21:39:15Z",
    "update_time": "2013-06-25T21:39:17Z",
    "state": "authorized",
    "amount": {
      "total": "7.47",
      "currency": "USD",
      "details": {
        "subtotal": "7.47"
      }
    },
    "parent_payment": "PAY-36246664YD343335CKHFA4AY",
    "valid_until": "2013-07-24T21:39:15Z",
    "links": [
    {
      "href": "https://api-m.sandbox.paypal.com/v1/payments/authorization/2DC87612EK520411B",
      "rel": "self",
      "method": "GET"
    },
    {
      "href": "https://api-m.sandbox.paypal.com/v1/payments/authorization/2DC87612EK520411B/capture",
      "rel": "capture",
      "method": "POST"
    },
    {
      "href": "https://api-m.sandbox.paypal.com/v1/payments/authorization/2DC87612EK520411B/void",
      "rel": "void",
      "method": "POST"
    },
    {
      "href": "https://api-m.sandbox.paypal.com/v1/payments/payment/PAY-36246664YD343335CKHFA4AY",
      "rel": "parent_payment",
      "method": "GET"
    }]
  },
  "links": [
  {
    "href": "https://api-m.sandbox.paypal.com/v1/notifications/webhooks-events/8PT597110X687430LKGECATA",
    "rel": "self",
    "method": "GET"
  },
  {
    "href": "https://api-m.sandbox.paypal.com/v1/notifications/webhooks-events/8PT597110X687430LKGECATA/resend",
    "rel": "resend",
    "method": "POST"
  }]
}

Note: To get the latest resource from PayPal, navigate to the HATEOAS self link from the received payload.