New background audio feature

Hello everyone, in the attached file I created an audio volume using Javascript. Everything works fine when the audio is inserted directly into the slide, but when I add the Slider and triggers on the master slide the volume stops working using the new background audio feature. Can anyone help me with this please? Thanks!
Here's the Javascript I'm using.

var player = GetPlayer();
 var _volume = player.GetVar("HotspotSliderValue")/10;
 console.log("vol: "+_volume);
                     

var allAudios = document.getElementsByTagName("audio");
if (allAudios[0].volume >= 0) {
 for (var a = 0; a < allAudios.length; a++) {
 allAudios[a].volume = 0.5;
 }
 }