Hello all,
I got recently a problem, and I will be very thankful for assistance.
I am a relative novice and almost ignorant in this field, so I am mostly use the services of a freelancer from Fiverr. Even so, it looks that he cannot fix it too.
I am on 1.5.4
At Search Console (Google) I get the following message: /https://www.petrutech.com/ Sitemap is HTML

Your Sitemap appears to be an HTML page. Please use a supported sitemap format instead.

The sitemap is not HTML, and it was "produced" using Google (as far as I know).

I think that I found the problem, but I don’t know how to fix it:
If you type http://www.petrutech.com/sitemap.xml or https://www.petrutech.com/sitemap.xml it works fine.
However, if you write www.petrutech.com/sitemap.xml it shows an error.
I don’t know if it is a canonical or redirected error, but I assume that Google gets an error from the www, without the http or https.
It also may be in the site cache…

I will appreciate any help / assistance