Wondering why you're unable to add a guest user from your Slack workspace as an admin for Donut Onboarding or Pairing channels? 

Unfortunately, Slack doesn't let guest users sign into Slack apps, so there's no way for us to give access to the dashboard to guest users. If you'd like to add a user as an admin, you'll need to make them a full user first.

You can read more about Sign in with Slack here.