Then you have seen incorrect configurations where people have tried it without success. I don’t know of any way to use FS20 devices with Home Assistant unfortunately.
Edit: this might work: GitHub - helpsterTee/cul-hass-mqtt: A lightweight Python3 parser for publishing FS20 messages from a serial CUL device to home-assistant using a MQTT server or GitHub - hobbyquaker/cul2mqtt: Interface between Busware CUL and MQTT