Hello, the WHMCS Slack notification module currently uses channels exclusively so that notifications can only be sent to public channels. The code does not use the group.list or conversations.list API commands to search for particular groups. I think if I had the option of sending tickets to private groups it would be a good idea because we could use the work groups that only the support staff has access to.
Version 7.7 has now reached public beta, which includes this feature.
Please join us during the pre-release testing period and provide your feedback in our dedicated beta community board: https://whmcs.community/forum/462-v77-beta-discussion/