Hi @ailaine
There are probably empty lines in one of these files
In wp-config.php (WordPress) there must be no blank lines before the <?php or after the ?>.
Also in the Functions.php of the WordPress theme, there must be no blank lines before the <?php or after the ?>.
This causes 2 blank lines to appear before the <!DOCTYPE html>, resulting in an error message
Have a look at the source code of your page
You use Yoast anyways, why you have a second xml creation plugin from Bestwesoft?
https://xxxxxxx.com/sitemap.xml
Could be a conflict.
Also where is the forum?
https://xxxxxxxx.com/affiliates-faqs/sitemap.xml goes to
https://xxxxxxxx.com/wp-sitemap.xml
and not where your capture shows. All those are NOT from wpForo.
WpForo sitemap is:
(for example)
https://wpforo.com/community/sitemap.xml