Webhook Callbacks

What are Webhooks?

Webhooks allow you to keep your application in sync with FreshBooks. You can subscribe to FreshBooks Webhooks to receive real-time notifications from FreshBooks to your application.

Webhooks are a simple mechanism for sending notifications between APIs using HTTP POST callbacks. Webhooks allow you to specify a URI that you would like FreshBooks to POST information to any time certain events happen in a system. For instance, if you would like to receive a notification every time one of your users creates an invoice in FreshBooks, you can register a callback for the invoice.create method.

FreshBooks does not currently guarantee the speed at which a webhook is delivered after an event has occurred, and delivery could range from a few seconds to several minutes.

Access Requirements

Registering WebHooks

Webhooks can be created with a POST to the callbacks endpoint. In order to ensure that you are the true owner of a callback URI being registered, we’ve implemented a verification mechanism. When a callback is first registered, we will automatically send an HTTP POST request containing a unique verification code as well as a unique id for the callback record being verified. Simply send the verification code and the callback id back to us via a PUT to the callback API and notifications will begin being sent to your registered callback URI (see example on the right). You can ask us to resend the verification code at any time with a PUT call containing a resend variable in the body.

NOTE: You may want to consider storing this verification code for future use, as it will be used as the secret to calculate signatures used to verify webhooks are from FreshBooks (see below).

Searches / Filters

Field Descriptions

Receiving Webhooks

When an event of the type registered occurs, FreshBooks will send a POST request to the registered URI with the following form-urlencoded parameters:

• http://your_server.com/webhooks/ready?name=invoice.create&object_id=1234567&account_id=6BApk&business_id=6543&identity_id=1234user_id=1

This means that the user with identity_id 1234 in the account/business created an invoice with the id 1234567. Because some FreshBooks resources use account and others business (See Identity Model), both the account_id and business_id are provided. You can then call the FreshBooks API invoice resource, passing in invoice_id 1234567 in order to get details about the invoice.

Failed Callbacks

Once your Webhooks are set up and verified, you will start receiving events. If FreshBooks receives anything other than a 2xx HTTP response code (including 3xx HTTP redirection codes) we will consider the attempt as failed. Webhooks HTTP POST requests have a ten second timeout set, and if there is no response within this time then the attempt is also considered failed. To avoid timeouts, consider deferring app processing until after a response to the webhook has been sent.

Failed requests will be retried periodically. After several failures, the message will be dropped and no further delivery attempts will be made.

If the webhook URL registered returns only failures over a long period, FreshBooks may disable the webhook. It can be easily re-enabled later by resending the verification token.

Verifying Webhooks

Each Webhook sent by FreshBooks includes a header, X-FreshBooks-Hmac-SHA256, with a base64-encoded signature generated using with the data sent in the request and token originally sent in the web hook verification process as a secret.

When you receive the webhook, you can verify that it came from FreshBooks by computing the signature and comparing it against the header.

The signature is calculated by FreshBooks by hashing a UTF-8 encoded json string of the parameters using the verifier key, then base64 encoding the result.

import base64
import hashlib
import hmac
import json

msg = dict((k, str(v)) for k, v in message.items())
dig = hmac.new(
    verifier.encode("utf-8"), 
    msg=json.dumps(msg).encode("utf-8"), 
    digestmod=hashlib.sha256
).digest()
return base64.b64encode(dig).decode()

A few things to note:

• We cast all values to a string
• The python json.dumps method yields json in the form of {"key": "value", "key2": "value"}.
  Note the spaces after each : and ,. If you’re json stringify does not include those, it will result in a different signature.

See some language examples on the right.

Valid Events

Events in FreshBooks are identified by the combination of a noun and a verb (i.e. invoice.create). You can subscribe to all supported events related to a noun by using only the noun part (i.e. invoice). Note that callbacks are notified when these events occur from within the FreshBooks application or from another application that uses the FreshBooks API.