Thank you for taking time to help. Now i know. And can help others. Lol
Super man.
Ok the light works but it seems my fanspeed topic does not work. Will check some more
I’d check with a TransformationPattern like: =“JSONPATH:$.FanSpeed.Fan”
This works:
Type number : mstFan "Master BD Fan" [ stateTopic="stat/sonoffMSTfan/RESULT", commandTopic="cmnd/sonoffMSTfan/FanSpeed", transformationPattern="JSONPATH:$.FanSpeed" ]