Hi Eduardo, I’ve entered both your sitemap.xml and your sitemap-posttype-post.2019.xml in the online validator tool https://www.xml-sitemaps.com/validate-xml-sitemap.html and both are valid.
Maybe the error is an old one and will disappear after a while. Or you can try removing the sitemap from your Search Console and then submit it again. Hopefully the spider will re-validate it then.