Hi Penny,
I had a quick look and the origin of the issue is that you have set a wrong site URL in your WordPress configuration.
The Sitemap Generator uses the default URL which you have set in the WordPress configuration. For your site this is currently “https://www.shannarawiki.net/wp/”. If I open this URL, I just get an error.
Is is possible that you moved your site from this URL to https://www.shannarawiki.net/ recently?
If so, then you have to adjust the configuration. You find the option in the general WordPress settings. I currently have no English WordPress installation, so I could not tell you how it is named exactly, but it should be something like “Settings” -> “General” -> “Site URL”… Please let me know if you have trouble to find it.
Best regards,
Marco