I've three Google mail accounts and their calendars on my Tbird installation. Two work and the third does not as appointments saved in Gmail don't show and new appointments don't show to accept or refuse. A recent appointment request came in a with a header "No writable calendars are configured for invitations, please check the calendar properties". But what should I be checking for when I get there? The URL for this accounts gmail calendar looks correct when I look at Gmail settings. Any ideas how to fix? I'm on v. 78.9.0 and all updated. I do not see Lightning in the Manage Your Extensions nor in the Thunderbird Options box (it does show Calendar but nothing about Lightning). Thanks!