I've about reached my breaking point related to Gio cal vs. G-cal and the unhealthy frienemy relationship they have had over the past couple of years.   You can subscribe to the a couple of our Gio sub-group cals from and G-cal and they the work just fine and others just will not do squat. Gsuite account, non-gsuite account, old account, new account, I just cannot get stuff to work in any consistent fashion.  The community is in disarray at this point given the fact that so many folks do not use Gio natively and I simply have run out of ideas.