The HTTP Protocol uses number codes to notify of errors. I’m sure you’ve seen a 404 error before when you try to visit a page that doesn’t exist. These codes are VERY helpful when working with APIs because they can help you know what is going on. If you don’t get the response you are hoping for from the API (200), then you can look at the code to see if the problem was that you have the wrong url (404), Your request is malformed (400), you are not authenticated / missing token (403), or another common error.
Here are some resources to learn about status code: