Step-1 : Cick on to (+) button besides "Subscribed Calendars" dropdown in ZA calendar.
Step-2 : Name and URL to be filled into the pop up screen which appears on clicking (+) button. Give any name. For URL open google calendar in another tab of your browser.
Step-3 : In google calendar select the logged in users calendar which will be there under "Settings for my calendars". As shown in screenshot logged in google user is zyprr prod.
Step-4 : There will be a URL provided under "Secret address in iCal format". Copy the URL and paste it in the URL input box mentioned in Step-2. After few mins the syncing will start. This is from google calendar to ZA calendar.
Step-5 : For other way syncing from ZA to google, go to google calendar and click on to the (+) button beside "Other Calendars"
Step-6 : The submenu which appears, click "From URL". A pop up screen will appear which will have an input box.
Step-7 : There will be a "Calendar URL" visible in the ZA calendar at the bottom
Step-8 : Copy that URL and paste in the URL input box mentioned in Step-6. Syncing will happen from ZA to google calendar.