whisperwow Ok, I see. Looks like this extension can't handle forums installed in a directory (i.e. your site.com/forum). I thought it could, but I guess not. The JavaScript included isn't pointing to the exact right spot. If your forum was installed at forum.yoursite.com or yoursite.com, it would work.
Maybe one day a developer here will contribute to this extension and help fix that. 😸 Or, it's always possible that I'll find the energy one day to figure it out. It's just not a priority for me at the moment.
Instead, because it's faster and easier for me personally, just like I did with the audio bbcode for you, I made a version for your forum. Hard to explain, but doing this is much faster for me than re-doing the existing extension. So, remove the existing one, and install this instead:
composer require 2nrwls/flarum-inline-audio:"*"
also run:
php flarum cache:clear