There are many mp3s on the site, all of which are working, including the one that I can no longer add to PowerPress. It is already on the site here, https://www.carryduffbaptist.org/sermons/good-foundations-churches-and-the-church/, and it still plays just find. I deliberately tried to add a new page with the same file to ensure that the files properties and permissions wouldn’t be a factor.
The only thing that has changed is my ability to add this file, or any, to Powerpress. Is there any reason why the file would be playable, both directly and through the WordPress site, and yet not selectable in the plugin?