The important thing about adding Google Calendar to CampLegal is every user in the firm must go through this process. Also, whatever Google Calendars the firm wants to use, those calendars must grant permission to those users via Google Calendars → Settings and Sharing setting.

Everyone must select their own Gmail account that has access to the Google Calendars and Authorize within CampLegal.
Go to the drop down under your name and click Settings:
Select Apps then click the Connect With Google button:
Select your Gmail account. Gmail account cannot be shared in CampLegal, the feature will not work correctly for the second user, this is a Google limitation.
If there’s a warning about the app not being verified please click advance and continue to CampLegal.com. We are in the process of getting verified, just a formality.
Select Allow for the next few Google screens.
You will be redirected back to CampLegal.
Logout and Log back in.
Now you have access to your Google Calendar in CampLegal