The problem is exactly what I explained to you above and what was explained at that link. You're trying to autoplay the audio before the user has interacted with the page. If you move the:
<<audio "start" play>>
to the "End" passage, then it works just fine fine after you click the "Continue" link which takes you to the "End" passage. This is because, by clicking that link, you've now interacted with the page.
You just need to have the user interact with the page before you can play any audio.