The 'Email already in use' error occurs when you are using the incorrect login option, and means that your Google email is already associated with a Facebook or Apple ID account.
  1. Return to the main login screen. You may need to click the Other Options button at the bottom of the screen to pick a non-Google option.
  2. Select a different login option (i.e. Facebook or AppleID)
  3. Log in using your usual email.