Hello @anshverma14,
Thank you for contacting support.
If you visit the /sitemap-index.xml URI on your site (or any of the sitemaps under it, such as /post-sitemap1.xml), and view the source code, you can see that the XML sitemap itself is working, but the linked XSL file is not – /main-sitemap.xsl returns a 404. We can only access that with the direct URI that looks like this: /?xsl=main.
So the issues are basically that /sitemap.xml should redirect to /sitemap-index.xml and /?xsl=main should be rewritten to /main-sitemap.xsl (the rewrite pattern looks like this: '/([a-z]+)?-?sitemap\.xsl$/' => '?xsl=$1').
These issues are most probably related to your server configuration. Please get in touch with your hosting provider about these.
We’d like to add that the only purpose of the XSL file is to make the sitemap “human-readable” so in terms of SEO it doesn’t make a difference. Google will still see the sitemap correctly, even without the XSL.
In other words, these issues will not hurt your SEO.
Hope this helps clarify your doubts.
Don’t hesitate to get in touch if you have any other questions.