I had same issue , got that "simon says skill bla bla " error even hosting it myself , i know the file is encoded perfectly as i used ffmpeg and the settings others provided . And i didn’t want to adjust my HA nginix proxy host config just for a simple mp3 file making the rest of the setup use a insecure dated config .
Solution ! ended up using https://jukehost.co.uk/ to host the file , works great