what might be the issue in this particular case. It might be something wrong with the connection between the MQTT broker and the client.
If you want to understand how this protocol works and how a correct connection is established, then I can redirect you to this article: https://cedalo.com/blog/mqtt-connection-beginners-guide/. It starts with the simplest definitions and then explains the connection itself and the CONNECT and CONNECT data packets.
There’s also the Cedalo forum that’s dedicated to tackling Mosquitto tech issues specifically.
