can’t get a valid feed

Hi!

I can’t get a valid feed and I don’t know what to do.
– tried a different theme
– tried to deactivate all plugins
– when I used: https://www.greetjegreetsyou.com/?feed=rss2 I got a pop-up, subscribed and got the postheaders in the list at my browser, but feedburner couldn’t validate.
– uploaded feedburner_feedsmith_plugin_2.3 and couldn’t get it activated. Got the message: The plugin does not have a valid header.

It’s here where my knowledge ends and I need help.
Please…

Thanks!

Greetje
https://www.greetjegreetsyou.com
https://www.greetjegreetsyou.com/?feed=rss2