Well congrats 
Now define a very simple testing item:
Switch MQTT_Test "Testing..." { mqtt="<[broker:testing/mqtt/topic:state:default]" }
With this one in place you should be able to do a first tst. Use your mqtt.fx to publish the Message “ON” to Topic “testing/mqtt/topic”. Check the log once again!
How did we do this just now? See: http://docs.openhab.org/addons/bindings/mqtt1/readme.html#item-configuration-for-inbound-messages
If everything works as expected you can now start to define specific items for your Sonoff. Once again, don’t bother with Espeasy. Go Tasmota:
- ITEAD Sonoff switches and sockets - cheap ESP8266 Wifi+MQTT hardware
- GitHub - arendst/Tasmota: Alternative firmware for ESP8266 and ESP32 based devices with easy configuration using webUI, OTA updates, automation using timers or rules, expandability and entirely local control over MQTT, HTTP, Serial or KNX. Full documentation at