Executing ServiceConnect["GoogleCalendar"] opens a Google login form in my browser, but after selecting my account, I get this message:

It reads "Access blocked: wolfram.com has not completed the Google verification process. wolfram.com has not completed the Google verification process. The app is currently being tested, and can only be accessed by developer-approved testers. If you think you should have access, contact the developer. If you are a developer of wolfram.com, see error details. Error 403: access_denied"