Plex ignores custom theme

I added a custom MP3 theme named “theme.mp3” to the show’s folder and I have Use local assets checked as well as Play Theme Music and Local Media Assets. I’ve reset the metadata for the show multiple times, and I looked at every online guide I could find and it still plays the default theme music for the show and not the custom one I added to the folder. I’m new to Plex so maybe there’s something I’m missing?