This error message would mean the subscriber is technically part of your list, but their status is "Unconfirmed."
What does this mean?
Unconfirmed subscribers are emails from signups coming from a form with double opt-in enabled and that haven’t yet confirmed their subscription to your newsletter.
⚠️ It's possible to manually confirm a subscriber. But, you should only consider this if they have contacted you directly confirming they wish to subscribe to your email list.
How to manually confirm a subscriber
How to manually confirm a subscriber
Go to the Subscribers tab and search for the email address
Once found, click on the email address to direct you to the subscriber's profile
From there, click Actions > Subscribe
