protected function getMessage(string $url): ?string
    {
        $response = wp_remote_get($url);
        $responseCode = wp_remote_retrieve_response_code($response);

        if (! is_int($responseCode)) {
            return 'Unable to reach ' . $url;
        }

        return ($this->expectedStatusCode === $responseCode)
            ? null
            : $url . ' returns ' . $responseCode;
    }