Issue is not really that we need a better message, nor should this simply be an enhancement to improve the message, there is certainly a bug to be fixed.
Our scenario is adding a person to a Space, who has participated in Webex Meetings in the past, but does not have a Webex Teams account; causes the error. (see: TAC Case # 688719386).
As a workaround, adding a person through https://teams.webex.com/ instead works fine.
Expected result is that an invitation (on Enter) is sent to new persons through Teams website or Teams client alike.
