RSS feed validity

I use Mozilla Thunderbird 68.9.0 for my feed reader, but I can't get this site using it.

It fails validation as shown here: https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Fwww.blackhatworld.com%2Fforums%2F-%2Findex.rss

Sorry
This feed does not validate.

• https://validator.w3.org/feed/check.cgi?url=https%3A%2F%2Fwww.blackhatworld.com%2Fforums%2F-%2Findex.rss#l1, column 1: XML parsing error: <unknown>:1:1: XML or text declaration not at start of entity [https://validator.w3.org/feed/docs/error/SAXError.html]
  
  <?xml version="1.0" encoding="utf-8"?>
  ^

Source: https://www.blackhatworld.com/forums/-/index.rss

1. <?xml version="1.0" encoding="utf-8"?>

Thank you!

I looked into this issue a while back. I think it was caused by the whitespace at the beginning of the first line of the rss file.

Anyway, it's not something I can edit. I'll try bringing it up this week to see if it can be fixed as it's been brought up a couple of times before.
https://www.blackhatworld.com/seo/rss-feed-of-bhw.1024306/#post-12683950
https://www.blackhatworld.com/seo/rss-feed-of-bhw-not-working.1046590/#post-11284219