I can't add users to Slack channels directly. However, if you're referring to adding someone to your Clay workspace, you can invite them by going to Settings → Team, clicking + Invite, entering their email address, selecting their role, and clicking Send invite.
If you need help with a specific Slack channel access issue, please request human assistance by clicking on "Talk to a person."
I've just sent an invite over to the email provided. Here is the invite link below as well.
Please let me know if you're still having issues here and how I can help!