Check your XML sitemap
Paste the sitemap. Everything checkable without fetching the URLs is checked, and nothing is uploaded.
Paste a sitemap to check it.
What makes a sitemap invalid?
The common ones: relative paths instead of absolute URLs, URLs on a host other than the one serving the sitemap, more than 50,000 URLs or 50MB uncompressed in one file, and lastmod values that are not W3C datetime. Each of those makes a search engine either reject the file or quietly ignore part of it.
Does priority actually do anything?
Google has said it ignores it. It was always relative to your own URLs rather than to the web, so giving every page the same value carries no information at all. Leaving it out entirely is fine.
Should every page be in the sitemap?
Every page you want indexed, and nothing else. Listing URLs that redirect, 404 or carry a noindex tag spends crawl budget to tell a search engine about pages you do not want it to have. A sitemap full of dead URLs is worse than a short accurate one.
Why does lastmod matter?
It is the main signal a crawler uses to decide what is worth revisiting. An unparseable date is ignored, which loses the signal, and a date that updates on every build whether or not the page changed trains the crawler to ignore it.
Other tools
This tool checks one page at a time. Visorank does the same work across every page on your site continuously, and shows you which queries people actually search rather than estimates.
What Visorank does