Hello,

having a look at your website source code it seems that the problem is due to a misconfiguration of the website.

Despite the fact that you have added a domain redirect in the htaccess from https://www.thenomanssky.com to https://thenomanssky.com the Joomla configuration seems to have still hardcoded the www version https://www.thenomanssky.com everywhere (see attached image). Obviously this affect the backend functionalities of JSitemap like seo spider, etc that are javascript based app blocked if the domain is different. If you access the backend using https://thenomanssky.com/administrator and the request is done to https://www.thenomanssky.com the script will be blocked.

Ensure that the configuration.php of Joomla has the $live_site variable empty as by default and that there are no other plugins forcing joomla to the www version of the website.