It is working again now.
Apparently there was an outage. Maybe Jessica can comment on the duration. ;-)
There was another problem though. My password had a special character in it which works great on the web site, but the app silently accepts it without complaining. Then the logon fails. After Jessica kindly pointed this out in a PM, I changed my password and all is well.
I did ask that Onstar modify their code to disallow special characters in password setup so this doesn't cause problems for anyone else.
I give Jessica a thumbs up
in responsiveness and attitude!