Lightbox Video opens but no video plays or seems to be connected

How To
1

I’m trying to create a video lightbox that opens when the thumbnail image is clicked. Everything seems straight forward, but when the thumbnail is clicked the lightox opens, shows a video player, but nothing plays or seems even connected. The play button in the video lightbox is greyed out and cannot be clicked.

This is my setup (the yt link works fine when pasted into the address bar):
image
PS: I’ve also pasted just the root of the YT url - https://youtu.be/Sz9-3EBhHSQ - with the same non-playing results.

But this is what pops up:

image
image1382×823 38.6 KB

There don’t seem to be any other options to check. Any suggestions?

Thanks!