hey, just to be clear are you using the tool at https://kool.tools/bitsy/tools/bitsymuse-ui/ for multi-room audio?
for this there are two important things to check: 1. you need to select all the audio files at once through the "select files" picker 2. you should make sure the audio files are located beside the html file when you try to play (the "export zip" option will do this for you)
if this doesn't help i recommend joining the bitsy discord where there are more people that can help you work it out, but i don't mind continuing to try to work it out in these comments if that's better for you
good luck, let me know how it goes