RSS Feed Issue: Unknown Namespace

Hi everyone,

I’m having a huge issue with linking my RSS feed in Mailchimp. When I set up a campaign, it says my RSS feed is not valid. I’ve contacted Mailchimp and they said it’s this error:

line 33, column 0: Use of unknown namespace: com-wordpress:feed-additions:1 (6 occurrences)

I contacted Bluehost and they said my RSS feed is valid, but Mailchimp said it’s valid but a namespace needs to be listed. I’ve deactivated my plug-ins, ran the Health Check plug-in, tried the RSS repair plug-in, and switched my theme to default – nothing worked.

How would I list a namespace in my RSS feed? I have no idea what that means.

The page I need help with: [log in to see the link]