Works Perfectly

Is you follow the instructions in the previous commenter’s posts, it will work like a charm. This is the one that got me up and running:

If you copy and paste the shortcode from that tutorial page, it won’t work. That example has “smart quotes” (ie, “ and ”) instead of regular “straight quotes” (").

Following the op’s link above, and turning on Chrome’s devtools and looking at the Network tab, I can see that’s his problem too. The call to googleapis.com has extra characters surrounding the calendar id. Those extra characters are the “smart quotes.”

Just retype the shortcode (type the quote characters instead of copying and pasting from the tutorial) and give it a try.