Okay, final tips: also subscribe to the error events. Even just subscribing to all your application’s events using +/+/+/events/# and then passing all messages to a log file can be of great help while debugging at some later time. (Though you won’t get an error if the configuration of your topics is wrong; you’d just not receive anything then.) Also, don’t forget a catch node for errors that occur in Node-RED itself.
See an example in Why is Node-RED integration no longer supported?