Unfortunately I had connected Odoo to the wrong Google Calendar API.

I deleted the old Client I/D and Client Secret, disabled the Google Calendar Sync, restarted the odoo server and enabled Google Calendar with the new credentials.

Now I am not able to add any appointment to the odoo calendar.

Trying to add an calendar event results in: (translated) An error occurred while generating the token. Your authorisation code may be invalid or already expired [unauthorised_client].

Original: Während der Generierung des Tokens ist ein Fehler aufgetreten. Eventuell ist Ihr Autorisierungscode ungültig oder bereits abgelaufen [unauthorized_client]

How can I delete the old sync information and the Google-Registration completely to start over?

It seems not to be sufficient to disable the calendar sync in preferences. Thank you for your topps!