If someone could help to understand what the problem is would be very grateful. I and my team we are on a free trial of the Jira (Cloud). At some point few users of our team just became deactivated. I as org admin can`t reactivate them back.
Anyone knows why is that? What can be the reason? Thanks!
Welcome to the Atlassian Community!
Atlassian Cloud use "Atlassian accounts" for access, such as the account you are currently using to post here. (Unless you're using Atlassian Access).
Atlassian accounts belong to individuals or the organisation that has claimed the domain their email address is in.
They're external to Jira, not a part of it. You don't create an account in Jira, you tell Jira that an external account can log in and act.
So, what Jira is telling you here is that someone has deactivated (probably in preparation for deleting it) these accounts. So you can't add them to your Jira, because they're not usable.
You will need to get those users (or their organisation) to re-activate their accounts. A quick test of where the problem might be is to try to log in here in the Community (not to do anything, just it tends to give you a different and more helpful message when an account has been deactivated)