When you select the Google calendar you will see the following message.
(the x’s will be alphanumeric characters)
Cancel / Add”
Click the ‘Add‘ button
You may briefly see a message at the bottom of the screen “Calendar created – fetching events in the background”.
If you now look at the Google calendar main menu (‘hamburger’ icon top left), under ‘Other calendars’, you will see ‘Caltrics’ listed.