Sitemap can be read, but has errors

I recently did some changes to my sitemap because i updated my website to support two languages but now i get an error when submitting the sitemap and i don’t see where the problem is.

Your Sitemap or Sitemap index file does not properly declare the namespace. 
>     Examples >     Line 5 >     Parent tag: >     url >     Tag: >     link        <urlset xmlns:xsi="" xmlns="" xmlns:xhtml="" xsi:schemaLocation="">     <url>     <loc></loc>     <xhtml:link rel="canonical" href=""/>     <xhtml:link rel="alternate" hreflang="el" href=""/>     <xhtml:link rel="alternate" hreflang="el-GR" href=""/>     <xhtml:link rel="alternate" hreflang="x-default" href=""/>     <xhtml:link rel="alternate" hreflang="en" href=""/>     <lastmod>2020-02-25T12:41:35+00:00</lastmod>     <priority>1.00</priority>     </url>              ````````           </urlset> 


Tried this method like the Google Documentation says so

<urlset xmlns=""   xmlns:xhtml=""> 

Although when using xmlns:xhtml="" converts the xml to plain text, changing http to https outputs the xml correctly and does the work but i have read you must use only http to avoid my issue, honestly this it too confusing.