To communicate with slack, you need to allow some permissions, for this go inside the slack app and navigate to the 'OAuth & Permissions'-->'Scopes'-->'User Token Scopes' and enable permissions such as 'mpim:read, im:read, groups:read, channels:read, chat:write, chat:write:user, chat:write:bot, users:read'.
To communicate with slack, you need to allow some permissions,
for this go inside the slack app and navigate to the 'OAuth & Permissions'-->'Scopes'-->'User Token Scopes'
and enable permissions such as 'mpim:read, mpim:history, im:read, im:history, groups:read,