The API returns HTTP status codes as may be expected. Here is an overview of the most common ones:

200 OK The request succeeded normally
400 Bad Request The request sent by the client was syntactically incorrect
401 Unauthorized The request requires HTTP authentication
403 Forbidden The server refused to fulfill the request
404 Not Found The requested resource is not available
500 Internal Server Error Indicate an error inside the server which prevented it from fulfilling the request

Incase of an error, M/Monit might provide more details in a JSON object returned in the response.

{
    "error": "SQLException: Connection not available"
}