Insert went wrong: Error refreshing the OAuth2 token, message: '{ "error" : "inv

Hi

I have been having trouble with the Apointments+ plugin since 12. of July, it will no longer sync with my Google Calendar.

I have tried creating new Google API, followed the guide from scratch but I can't get it to work. Everytime following message will appear in the log:
"Insert went wrong: Error refreshing the OAuth2 token, message: '{
"error" : "invalid_grant"
}'"
Hope you can help
Best
Mikkel