//..

    operation.attempt(function(currentAttempt) {
        // Make an HTTP GET request to http://httpbin.io/status/500
        axios.get(URL)
            .then((response) => {
                // If the request is successful, resolve the Promise with the response body
                cb(null, response.data);
            })
            .catch((error) => {
                // If there's an error, check if retry is allowed.
                if (operation.retry(error)) {
                    return;
                }

                // If all retry attempts are exhausted, reject with the main error
                cb(operation.mainError());
            });
    });