You have an MQTT server, and sometimes you need to consult or browse “topics”.
I recommend installing the “smeagolworms4/mqtt-explorer” docker image, which will let you do all this and more.
Here’s a short tutorial on how to update the status of GPIO connectors from a Raspberrypi to an MQTT server, using docker images.
You’ll be able to read the GPIO status, but also modify it if, like me, you have a relay connected to it.