Hamburger menu not working in mobile

Hi, on this site the hamburger menu doesn’t open in mobile view (I am aware that it is not secure, the owner has been to busy to get me access). I am not sure what’s going on, must be a js issue but I don’t know where to start. Thanks.

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

Not a webflow site so…