When I try to invite a team member on Slack to a channel, I see the following message:
Multi-channel guests may not appear below. Ask a Team Administrator to invite them.
How do I find out who is a Team Administrator on my team?
Go to https://TEAM.slack.com/account/workspace-settings
Or via the UI:
Go to your team's Slack webpage (i.e. https://TEAM.slack.com
)
You can get there by tapping the dropdown arrow then choosing one of the links below your team's organization such as "Customize Slack."
In the left menu, possibly under the hamburger (depending on screen size) select "About this workspace"
Click on the "Admins & Owners" tab
You will see a list of owners and admins on this page.