"moduleReadyEvent" not firing at all

Hello,

I have a web page that has an <iframe> of the captivate lesson that was published in captivate 8. I was able to access window of the iframe and attach an event listener like so:

// The <iframe> element that has the HTML5 lesson published from captivate.
var iframe = document.getElementById('captivate-iframe');
iframe.contentWindow.addEventListener("moduleReadyEvent", function(evt){
     alert('Captivate lesson ready');
     console.log('Captivate lesson ready');
     debugger;
});

But this event never fires. Nothing happens. Though, I'm able to access other captivate variables such as cpCmndPause and such to play and pause the video. But the ready event never fires. Is it only for certain versions of captivate?