Why it matters
The protocol requires fully qualified URLs on the sitemap's own host; others are ignored.
How to fix it
Build every loc from the production origin (site.url + path).
References
More seo rules
void seo reports 60 rules in this category. What search engines need from the raw response: status codes, titles and descriptions in <head>, self-referencing canonicals, one h1, crawlable links, Open Graph, icons, robots.txt and a sitemap with real dates.
robots-blocks-resourcesrobots.txt blocks JS/CSS needed to renderrobots-sitemap-directiverobots.txt has no absolute Sitemap: linesitemap-missingNo reachable sitemapsitemap-invalidSitemap isn't valid sitemap XML or exceeds protocol limitssitemap-lastmod<lastmod> invalid, in the future, or identical across entriessitemap-url-statusSitemap lists URLs that don't return 200 directlysitemap-url-not-indexableSitemap lists noindex, robots-blocked or non-canonical URLsduplicate-titleMultiple pages share the same <title>