I would like to add new message (in this case after registration of payment to invoice) to object (in this case invoice...) with Automated Action but i didnt find way how. 

I know i have to create new server action when invoice goes to status "Paid", but I am not sure how this action should be done. I tried some, but it didn't work. Is there somebody who could help me?

The reason is i just need to let know some people when invoice is paid, but I dont want to use "Send email" action, because i need to use also follower of that invoice.

Thank you!