error on line 2 at column 6: XML declaration…

I am trying to generate a sitemap for myself. Usually my experience with Yoast is rock solid but this time, I can’t seem to get an answer on what’s going on. I have run a conflict test in troubleshooting mode and have disabled all plugins except for Yoast, I’ve switched to a default theme, and this problem still persists. I am following the instructions on this article: https://yoast.com/help/xml-sitemap-error/

But it isn’t working. What’s my next course of action here?

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