From the documentation of the link you sent I see these actions needed:
Configuration:
- Need to set “mqttServer” to the HestiaPi IP
- Set “topic” to one or (if supported) many topics published by HestiaPi. Find the topics list here
- Leave HestiaPi authentication params as is because the MagicMirror module says it does not support authenticated messages.
For troubleshooting use your laptop and do that:
Confirm by subscribing from another laptop to all (#) MQTT IDs and listen for published messages while you play with your HestiaPi:
mosquitto_sub -h [HESTIA_PI_IP] -d -t hestia/#
[copied from here]