I found from here(https://www.hivemq.com/blog/mqtt-essentials-part-5-mqtt-topics-best-practices/) that
“$” can not be used when you publish a message.
And indeed I found this from the code:
public static final AtomicBoolean MQTT_ALLOW_DOLLAR_TOPICS = new AtomicBoolean(false);
And I want to ask if I can change it to true to let HiveMQ allow dollar-topics?