RSS feed problem using XSL style sheet

I have a problem with my entries RSS feed

The XML page cannot be displayed
Cannot view XML input using XSL style sheet.

I have tried to fix it by changing the nickname (as suggested in other posts) but that did not help.

The feed did work earlier but I can’t say when it stopped working.

Your help will be greatly appreciated

Here’s my blog:

https://www.halinagold.net/marketing

and the entries RSS:
https://www.halinagold.net/marketing/index.php/feed/

Thanks

Halina