iTunes won't validate podcast artwork.

I am not super computer savvy. I have resized my podcast artwork a million times to get it within the pixel and <500 kb requirements. I downloaded photoshop to make sure it was saving in RGB. I am seriously losing my mind. If anyone could please take a look and let me know if I am missing some something obvious? Feed is

https://feed.podbean.com/darklandspodcast/feed.xml

Thank you so much in advance.