Hey Darren,

I am sorry for the delay of this reply,

I've checked in your site, it seems like your current template conflict with bootstrap styling, you can take a look of my attached screenshot below.

if I unchecked that styling as I pointed it to, the pop up is work fine.

If you would like to quick fix for this, you can apply this following css in your template css file and see how it goes.

#jsn-master .modal {

	position: fixed !important;

}

But It would be best if you can consult with your template provider regarding this.