Why it matters
The Sitemap directive is how crawlers other than Google (Bing, AI search crawlers) find your sitemap; it must be an absolute URL.
How to fix it
Return sitemap: 'https://your.site/sitemap.xml' from app/robots.ts.
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-txt-missingNo robots.txtrobots-txt-invalidrobots.txt serves HTML, exceeds 500 KiB, or has unparseable linesrobots-blocks-allrobots.txt disallows the site for * / Googlebot / Bingbotrobots-blocks-resourcesrobots.txt blocks JS/CSS needed to rendersitemap-missingNo reachable sitemapsitemap-invalidSitemap isn't valid sitemap XML or exceeds protocol limitssitemap-url-invalidSitemap <loc> is relative or on another hostsitemap-lastmod<lastmod> invalid, in the future, or identical across entries