Cannot upload .mp3 file to wordpress media

you need to allow them to be uploaded in your media files.

you can add following code to your themes functions.php

function my_mime_types($mime_types){
    $mime_types['mp3'] = 'audio/mpeg';
    return $mime_types;
}
add_filter('upload_mimes', 'my_mime_types', 1, 1);

there is more information about adding new mime types in WP here: https://wpsmackdown.com/add-remove-filetypes-wordpress-media-library/#add-filetypes

And here a list of the mime_types: https://feedforall.com/mime-types.htm