Youtube lightbox not working

not sure what i am doing wrong. Vimeo link opens in lightbox but not the youtube link.

(a) href=”https://www.youtube.com/watch?v=XfLiXFc4LFE&feature=youtu.be”>Watch trailer (/a)

of course I enclosed the a tag in regular brackets so you can view the code, otherwise it was coming thru as a hyperlink

The vimeo link is exactly the same, just replace the url. What am I missing?

https://wordpress.org/plugins/responsive-lightbox-lite/