XML Sitemap generates 404 error page

…and when I input the URL generated (https://cmcsolicitor.ie/wordpress/sitemap_index.xml) in google webmaster I get an error of course.

I’m using this plugin to guide me through the process of improving my SEO – to make the job easier. I do not intend to disable all of my other plugins (which work great!) and/or to change from my lovely now theme (which works great too).

Short of that suggestion, is there a way to make this plugin do what it is supposed to do? Is there a troublshooting solution that might help me – no suggestion could be too simple or too obvious-sounding!

Thanks

https://www.ads-software.com/extend/plugins/wordpress-seo/