WordPress RSS Feed Not Validating

Every time I try to run my Web Site RSS Feed through the W3 Schools validator, or add it too iTunes connect, it says it can’t be validated.
here is the URL to the feed I am trying to Validate: https://www.willsdigitalworld.com/?feed=rss2&category=history
The error I am getting is as follows.
url must be a full URL: https://www.willsdigitalworld.com/podcast_media/jfk_assassination.mp3
The url I added to the enclosure tag is exactly how they say it needs to be written. so I am stumped on why I keep getting this validation error.
I can put the URL to the feed in iTunes and subscribe to it with no problems. but yet iTunes connect says it can’t be read.