[Plugin: YouTube SimpleGallery] Plugin links not working

OK, now I’m new to all of this WP stuff, but I’m slowly learning as I go.

I have installed & activated the youtubegallery plugin, along with shadowbox-js. I have linked the two together.

When I make a new post, I get the grey “video missing” thumbnail which is tall and skinny rather than square. When I hover my mouse over the link it gives me “https://www.youtube.com/embed/%3Ciframe%20width=” and upon clicking it, tries to load the page, but obviously that link is bad.

I even reinstalled the plugin from scratch, re-linked it to Shadowbox and used the default video links supplied in the readme:

[youtubegallery]
https://www.youtube.com/watch?v=cRdxXPV9GNQ


https://www.youtube.com/watch?v=S4aqM_wu6Ns
[/youtubegallery]

I’ve got to be missing something somewhere, but I’m totally stumped. Any help would greatly be appreciated.

https://www.ads-software.com/extend/plugins/youtube-simplegallery/