One button to set complete

Hi,
I'm sorry if this is on forum but i cant see answer
What i need to set/write in button to use join block for set complete "flag" to close "join function"


For now i have setup like this with error

You are getting confused msg.topic is not msg.complete

add a change node after button and
set msg. complete
to value of boolean true

You may benefit watching the essentials videos

Thank you E1cid - also i will look on videos..