Emails someone an invitation to join the connected Nexwin account with their own login. They become a team member once they accept; the link expires after 24 hours. Use add_team_member instead for a person who only needs to be bookable and won't sign in. The invitee starts with calendar access only; access to call history, the knowledge base or AI Setup is granted in the Nexwin dashboard. Executes immediately: the email is sent as soon as this is called, so check the address with the user first.