If you remember, HTTP statuses let you give someone some information about how the request went. Did it go well? Did it go poorly? That kind of thing. You can get a list of all the HTTP statuses available to you by going to httpstatuses.com. Here, you can view all of the statuses that you can set:

The one that's set by default by Express is 200. This means that things went OK. What we're going to be using for an error is code 400. A 400 status means there was some bad input, which is going to be the case if the model can't be saved. Maybe the User didn't provide a text property, or maybe the text string was empty. Either way, we want to send a 400 back, and that's going to happen. Right before we call send, all we're going to do is call status, passing in the status of 400:

todo.save().then((doc) => {
  res.send(doc);
}, (e) => {
  res.status(400).send(e);
});

With this in place, we are now ready to test out our POST /todos request over inside of Postman.