Home Assistant as aclear installation procedure for internal MQTT broker. It is an add-on which is well documented.

All you have to do is install this add-on clicking on the add integration button

Then you should look into the Add_on store to find the Mosquitto MQTT

Finally install and activate it 

Then you can find it into your integration page

Simply click to configure the broker and access the default configuration.

Your MQTT broker is ready to receive and lsiten to messages.

If you click again on teh configuration button then you even get a test page to send and listen to packets.

In this simple example I have tested the broker while manually sending a command message to my Rezodo GTW1 coil3 (topic field)

And with a JSON payload compliant with FDRS API

Then I can subscribre to this message and start listening the broker.

As soon as I click the publish button, the message is send and displayed in the received messge part of the screen.

Easy no ?

That's it your MQTT broker is installed and configured. But now we can do more!

You will need to create an account in Home Assistant for the GTW0 to be allowed to access this MQTT broker.

The credentials you choose must be entered into the fdrs_gateway_config.h as shown above.

This HASS account is a regular one which is preferably different from your personnal account.