Interesting that in setting up the Cal space - I needed to get an App specific password - which took me down a loop - over and over again. Did some searching and discovered that I am not unique.
The fix? Use Chrome - not Safari!
FTW
Safari breaks on one of Apple's own services!
Interesting - I just had my first ever meeting through cal.com - and discovered it also has video conferencing just built in ... went on for an hour - no disconnect at 40 minutes - stunned I tells ya. STUNNED!
... choose the app you want to integrate with cal.com and you are good to go.