I have been running into an issue lately when attempting to start Webex Meetings from the meeting notification in Webex Teams (the green "Now" button that launches the meeting next to the host/team entry), giving me this error:
BUT when I try joining from the embedded link in the meeting invitation email, it DOES work, although it seems to take an unusually long time even there. It seems that it thinks that a previously ended meeting is still in progress when launching from Teams.