Google Calendar / Fantastical

Last year I found a way to send Due Dates to Fantastical (on my phone) via GoogleCAL.
This no longer works, although I can still see the OLD reminders both in Fantastical/GoogleCAL, and delete them by removing the TAG from the Asana Task, which was how the integration worked in the first place.
Could someone please clarify:
• Was the method changed? Do I need to setup a specific “integration” – if so, which one?
• OR was this a premium ONLY feature that I discovered during the trial period?
• If “premium”, how is this feature described in the PLAN descriptions?

I’m struggling to assess the value of paying US$18/month Premium subscription for something I’m not sure I need - particularly when I see the message “some of your data has been removed - upgrade to Premium to restore” WHEN I don’t know “what data” OR feature has disappeared.