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.

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?