I'm trying to create simple aplication that will send me messege every day for example it can be "Hello world!". Is it even possible for facebook messenger extension to send message without being called? Where should I start? I mentioning about messenger extension because I would like this app to send message to group chat.
To sum up the comments: You can only send messages from pages to users (who contacted the Page first). There is no other API for user to user communication, or for communication in groups.