You can invite collaborators from the admin pane. From there, navigate to the Access tab then select Collaborators from the drop-down menu:
Now, click + Invite someone, fill in the form and hit Send invitation:
The person will then receive an email invitation join the hub as a collaborator. If they can't find it, ask them to look for message with the subject starting "You’ve been invited to collaborate".
💡 Tip: You must be the hub owner to be able to invite other collaborators.