Bad Request (HTTP 400)
The most common reason for receiving a a Bad Request (HTTP 400) is sending invalid input. (e.g., trying to create a cost code on a job that does not exist).
There are generally no guarantees around the response body of an HTTP 400, but HCSS APIs attempt to provide human-readable error messages so that you can fix the error.
If you're stuck, shoot us an email at firstname.lastname@example.org and we'll help you out.