Once you have uploaded your mp3 file, you should test it by adding a direct link from your index.html page.
From your Index.html page, the file is in the audio/ directory
You will need to spell the name of the file exactly right, including captials.
Inside the link it should say
Direct link to name of your file
Put the link on the Index.html page.
Save the page, then test the link.
The mp3 file should either load, or the browser should ask you to download it.
If you have an error, you have a problem with your code.
Make sure that you have the exact correct spelling of the file and path.
If you find a better way of doing this process, pass the word.