Google Calendar Sync problems

I can’t get the Google Calendar Sync to work.
I believe I have set it up correctly.
“Calendar API” is enabled in the Google Developer Project.

Picture of Client ID (Censored)

Picture of settings in Appointment Calendar (Censored)

Error Message when trying to “Connect Me”

I can give you admin access so you can have a look at it.

Thanks in advance.
Robert

https://ww.wp.xz.cn/plugins/appointment-calendar/