Shortcode not working in widget / popup

The plugin and its shortcode work a treat on pages / posts, and do what I need.

However, I now want to have the checker appear as an OnClick popup.

I’m using a popup plugin which will display shortcodes, but every time I add the shortcode to the popup it stops working and also screws the customised CSS of my site.

I also tried adding the shortcode to a sidebar widget specifically designed to display shortcodes and the same thing happened.

Site is under construction at the moment, but would be happy to give access to look under the hood if required.