Using Twilio's Usage Triggers, which we saw in Chapter 2, Exploring the REST API, allows us to build a circuit breaker.

In short, this will let us know when one of our subaccounts passes certain amounts of usage, which will help us detect possible abuse of our account, as well as mistakes in our code. It can even help detect abuse if we were running a multitenant app (that is, offering Twilio-based services to our users).

When our specified usage threshold is surpassed, Twilio will send a webhook to a URL of our choice. From this URL, we can perform a range of actions, whether that is sending ourselves an e-mail or even suspending the account in question.

For more details on Usage Triggers and how to specify them, head back to Chapter 2, Exploring the REST API. Here, we'll just run through a quick example of suspending an account if it spends more than $50 in one day.

We'll set up our Usage Trigger using the Twilio dashboard. To do this, first log in, and then switch...