Send message to slack channel through the flow

Hello, 

I am trying to send a notification to slack channel through salesforce flow.

But I am getting this error

This error occurred when the slackPostMessage action tried 
to execute the Slack API method: chat.postMessage. 
Error: channel_not_found. 

The slack channel exists. 

I have provided the channel id.

What am I doing wrong?

My username in salesforce is different than my username in slack, is that why?

or do I need to invite bot to the channel?How to do that?

Here is the screenshot of the action in the flow

#Sales Cloud  #Flows  #Slack Channel  #Slack