@williamsjohn. Thanks for posting. Well, to allow mp3 files, all you need to do is to add the mime type for mp3 to the list of “Permitted File types” in the Module Manager settings for Easy File Uploader module (EFUM). However, there is also the issue of how your server handles mime type detection. To find this out, go into the Module Manager settings for EFUM and copy and paste the Information and Diagnostics settings into a post in this forum, so that I can see it.
Now, you also have to be aware that mp3 has more than one mime type associated with it. You can either put all of them to be safe, or you can figure out which one your server detects and only put that one. Here is a link to mp3 mime types: http://filext.com/file-extension/MP3
You can also have a look at the documentation to on the website: https://www.valorapps.com/documentation/13-easy-file-uploader-documentation.html