RSS feed not validating

Hello. My tech skills are limited, so I don’t know if this is an issue with the Spacious theme or something else, but I hope you can help me. I use follow.it for emails about new blog posts for my four sites, using the RSS feeds to trigger new emails. Follow.it contacted me about their deactivation of the emails for The British TV Place, so I checked https://thebritishtvplace.com/feed and saw that it does not validate, although going to the URL shows the feed is active. It’s the same for https://thedownundertvplace.com/feed and https://theeurotvplace.com/feed. (Interestingly, https://theglobaltvplace.com/feed validates.) All four sites are published with the Spacious theme.

Do I need to do something on my end to get the three feeds to validate, so I can get the emails reactivated? Or is this something that needs to be handled by the Spacious team? Please advise. Thanks.

Linda