There are three response codes for all API calls: 200, 400, and 500. All user-errors return a 400 return, and all successful calls return a 200. If there are any errors that occurs server-side, a 500 error will be returned.
200 can return either a JSON object or nothing, depending on the API call.
400 will always return a JSON object with an error message and an error code.
500 will return a JSON object with only an error code.