How can Workspace members/admin can add more members/admin on a premium account?

[Deleted user]

I'm trying to invite people with a link and with just writing their E-mail address after clicking the blue button and this error above is popping out. 

Thank for your help,

Lauren. 

[Michael Pryor]

Are you part of a Trello Enterprise?  I think your Enterprise admins may have set up things so only users with your work domain can join the Workspaces in the Enterprise.