Podcast Feed Doesn't Validate

We’ve just transitioned the sermon player in our website from an old legacy player to your Sermon Manager plugin. We have it all set-up, however, using the feed validator linked in the podcast settings (https://gadietri.ch/1brBRLP) it shows that our feed is not validating. What do we need to change?

The feed listed in the settings page is https://olneybaptist.org/feed/podcast

https://www.ads-software.com/plugins/sermon-manager-for-wordpress/