Sitemap is html error

I recently changed my DNS server to cloudfare. After that when I am submitting my sitemap to search console, it is giving an error i.e. Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead. Kindly suggest what to do.

First check your sitemap in browser and then copy the address and paste it to search console. One reason for this error is wrong URL (i.e. naked domain instead of www). It would be helpful it you share your website address.