Node Red API error

Dear folks, I am new with Home assistant, which is why I find it easy to install Node-red. so fare so good.
but now i want to make a flow but i get the same Api error every time. See picture

Can someone tell me what I am doing wrong or what I should be looking at. thanks

Service is turn_on not switch.turn_on
Data can be empty in this situation.
GV

dear greengolfer, thanks for the tip. Works right away, great. Could you also explain to me how it is easiest to make a button on my dashboard for accessing a service?