MQTT Broker:

mosquitto

Install:

snap install mosquitto

Commands:

 mosquitto_pub -h 10.0.0.10 -t SENSOR3/+ -m '123' -d

ESPEasy trigger relay:

mosquitto_pub -t <devicename>/GPIO/2 -m 0                      #on
mosquitto_pub -t <devicename>/GPIO/2 -m 1                      #off

Gosund (switch power1):

mosquitto_pub -t <devicename>/cmnd/Power1 -m OFF
mosquitto_pub -t <devicename>/cmnd/Power1 -m ON

To send a message to a mqtt server:

https://diy.waziup.io/sensors/publish_using_MQTT/publish_using_MQTT.html

https://github.com/plapointe6/EspMQTTClient #authentication example!