How to send direct messages to a user as app in app channel

Question

How is it possible to send message in slack directly to the user, by user.id as application.

this application has scope: bot,channels:write,emoji:read,users:read,us

Answer 1

There is an alternative way to solve this, which can be more suitable if your app uses a bot to operate with Slack API.

You need to call chat.postMessage API method and specify channel argument equal to the user ID (e.g. U0G9QF9C6) you want to message and as_user argument is true. Important detail - ensure you are using bot access token (learn here how to obtain it).

Example:

curl -X POST "https://slack.com/api/chat.postMessage" -H  "accept: application/json" -d token=BOT_ACCESS_TOKEN -d channel=U0G9QF3C6 -d text=Hello -d as_user=true

In this way, your message will be always sent on behalf (name and icon) of your bot and will be display like a direct message in the app channel (YourAppChannel in the Slack sidebar).

Compared to the approach of @ErikKalkoken you have no need to create a channel in advance and as a result, keep track of its ID (it may be good or bad depending on your needs).