Hi Claire,
Yes, you have lots of JavaScript errors in your console on that page, pasted below:
Uncaught Error: Bootstrap's JavaScript requires jQuery
at bootstrap.min.js:6
jquery-migrate.min.js?ver=1.4.1:2 JQMIGRATE: Migrate is installed, version 1.4.1
YouTubePopUp.js:16 Uncaught TypeError: jQuery(...).YouTubePopUp is not a function
at HTMLDocument.<anonymous> (YouTubePopUp.js:16)
at i (jquery.js?ver=1.12.4:2)
at Object.fireWith [as resolveWith] (jquery.js?ver=1.12.4:2)
at Function.ready (jquery.js?ver=1.12.4:2)
at HTMLDocument.K (jquery.js?ver=1.12.4:2)
Fixing those should be the solution.
Peter