How can my bot server know INSTANTLY when someone installed the bot using Add-to-slack button?
ConversationUpdate should be sent any time a bot is added to a channel with a user in it. Are you not seeing that on install?
I use microsoft bot framework and a flask based bot server in my application.
When someone installs the bot, the Botframework stores the JSON POSTed by slack, including data like SLACK_TEAM_ID, SLACK_USER_ID and BOT_ACCESS_TOKEN. Its great, that from this point whenever, an user mentions or directmessages the botuser, the Bot Framework POSTs a JSON to the flask server.
What I would like is, right when the user installs the bot, the Bot Framework does a POST call to the flask server, so that I can (say) congratulate the user for installing my bot. 
In short: How to get my flask application notified as to who installs my bot as soon as they install it?