UPDATE:
After some playing around, I found a workaround:
After reading that iframes are deprecated on WordPress due to security reasons, I decided to try utilizing the embed code (iframe and script) within the plugin: Shortcoder. This generated a working shortcode that displays the quiz created. SUPER jazzed that I can use this awesome plugin now.
While this works for now, I would still like to request a closer look as to why the shortcode generated by the plugin itself does not work.
Thanks in advance!
Best,
Matty