API: Error handling
The API signals errors via standard HTTP status codes. This means that successful responses use a 2xx status code whereas errors are reported with 4xx or 5xx.
Applications and libraries that use TestRail's API are responsible for handling 5xx errors and are supposed to retry requests later in this case. 4xx errors are client-side errors and usually indicate an incorrect or incomplete request, e.g. trying to read a test case that doesn't exist or using an invalid request format.