Why it matters
Secure serving is a page experience signal and browsers mark HTTP pages as not secure.
How to fix it
Serve over HTTPS, redirect http:// to https:// in one 301/308 hop, and send Strict-Transport-Security.
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-snippet-restrictednosnippet or a very low max-snippet limits previewssoft-404Missing page returns HTTP 200 (soft 404)html-too-largeUncompressed HTML is over Googlebot's 2 MB fetch limitrsc-payload-ratioInline RSC flight payload dominates the HTMLorigin-redirectshttp:// or www/apex variant doesn't redirect to the canonical origin in one hophtml-lang<html lang> missing or not a valid BCP 47 tagviewportViewport meta missing, not device-width, or blocks zoomcharsetCharacter encoding not declared early