Sonoff Tasmota with MQTT Binding 2.4 (using config files)

Add mapping to your thing as openhab is not the same as tasmota.

, on=“ON”, off="OFF"

 Type switch : power     "Power"                  [ stateTopic="stat/sonoffpowr2-1/POWER", commandTopic="cmnd/sonoffpowr2-1/POWER" , on="ON", off="OFF" ]