For security reasons (read: in order to block annoying scam ads) most modern browsers automatically block audio unless you’ve already interacted with the page first.
Thus, generally it’s best to have some sort of opening “splash” screen first, and then only start playing any audio in the passages after that, since the user will have to interact with the page to get to that next passage.
If that doesn’t work, you should start your game, open the Developer Tools window (
CTRL+SHIFT+I in most browsers), and then look in the Console window to see what errors are reported there.
Also, while you can use FLAC audio in most browsers (currently ~%95.58 support, i.e. a bit over 1 in 20 will have a problem with it), I’d strongly recommend using MP3 instead (currently ~98.38% support, i.e. less than 1 in 60 will have a problem with it), as it’s much better supported. It’s best to save yourself and your users that extra bit of potential problems, assuming you plan on having 20+ users.
See the “Music” section of my Twine/SugarCube sample code collection for other details and suggestions regarding playing audio in your Twine/SugarCube games.
Hope that helps!