Hey @prasanth.pendham,
The authorization flow to call the GET /im/users/{{ USER ID }}/channels endpoint is a little different then the Chatbot Credentials and JWT flow.
In order to call the GET /im/users/{{ USER ID }}/channels (again, this endpoint is deprecated, but a new one is coming out soon.) you must use an OAuth App Type, or use a Chatbot App Type, and use the OAuth flow to get the proper access_token.
Basically once you install your Chatbot, you will use the code in the redirect url to request an access_token, and then you can use that to call the GET /im/users/{{ USER ID }}/channels endpoint. For example:
POST https://zoom.us/oauth/token?grant_type=code&code={{ code in redirect url }}&redirect_uri={{ your redirect url }}
Headers: "Authorization" : "Basic base64(client_id:client_secret)"
Will give you the access_token you need.
Let me know if you have any questions!
Thanks,
Tommy