There can be a variety of reasons why you may be unable to connect to your Google Calendar / Contacts account.

i) System Date & Time out of sync

When your system's date and time is out of sync, Google Servers may refuse to connect. Try this:

Open System Preferences > Date & Time. Make sure "Set date and time automatically" is checked. If not, check it, save it, quit and relaunch BusyCal and try again.

If it persists, rebooting your Mac should solve the problem. If not, try this:

1. If you're using Firefox or some browser other than Chrome / Safari, switch to Chrome and make it your default browser temporarily (we've seen issues on Firefox before).

2. Quit and relaunch your web browser.

3. Quit BusyCal.

Now try again.

ii) DNS cache needs clearing

Try this as a test:

1. Open your browser and paste the following link, it should open a blank page but should not show any errors: https://www.googleapis.com/oauth2/v4/token

If you see an error, your DNS cache needs to be flushed.

1. Open Terminal.app

2. Enter the following command and hit return

sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder

Now, try visiting the link above. If it succeeds, remove and re-add your account in the app in order to re-authenticate.

iii) Keychain Access related issue

1. Launch Keychain Access (in /Applications/Utilities). Select "All items" under Category in the left panel, and ensure "Login" is selected under Keychains at the top.

2. Type "BusyCal" (or BusyContacts, depending on the app you're using) into the search field and find all Google OAuth items that start with the name "BusyCal - Google...".

3. Select all of the matching items and press the delete key to delete them. This will delete the old keychain items and cause them to be rebuilt the next time they are needed.

4. Quit Keychain Access.

5. Launch the app and select View > Refresh Calendars (or type Command-R). A dialog will appear requiring you to Authorize with Google Calendar. Click the Authorize via Web Browser button.

6. In your web browser, login to your Google account if you're not logged in already, then click Allow to grant the app access to your Google Calendar. If you are syncing with multiple Google accounts, pay close attention to which account you are authorizing in your web browser and that it corresponds to the same account in the app.

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