404 error on sitemap

Tried to add the sitemap URL to comet cache but got a 404 error. Please see image
Also, the URL is not opening in the browser too, however, the full path is working /wp-content/uploads/sitemap.xml.

I am using LAMP. It requires an additional rewrite rule, as mentioned in this topic?

https://premium.wpmudev.org/forums/topic/smartcrawl-sitemap-404-error