How to prompt user first with a welcome message initially

I looked up, found this How to make bot reply first before user? - #3 by skjainmiah

but mostly people are saying that its specific to channels triggering initial intents, So i looked up more and found out that there is a default action known as action_session_start which we can override and send a message we want but I just couldnt override the action for some reason, it never gets overriden

my rasa version is 2.1.2 and sdk 2.1.2