Start with one URL, not the whole sitemap
Paste the full address into URL Inspection. Read the indexed status, last crawl, Google-selected canonical and whether the page can be crawled. Test the live URL if the report describes an older version. Save the result so a later check can show whether anything changed.
Check the page itself
Open it in a private browser window. A real page should return HTTP 200 with useful content. A login wall, server error, blank JavaScript shell or soft 404 needs fixing before another indexing request. Check for a noindex meta tag or X-Robots-Tag header, and make sure robots.txt does not block the crawler from seeing the page.
Check discovery and duplicates
Link to the page from a relevant page on your own site using a normal HTML link. Include its canonical URL in the XML sitemap. If several URLs carry the same content, pick the version you want to keep, link to it consistently and inspect Google’s selected canonical. A sitemap helps discovery; it is not an order to index.
Decide what deserves fixing
A checkout step, filter URL or duplicate print view may be correctly excluded. Focus on service, product and guide pages that answer a distinct search. After fixing the cause, request indexing for a small number of important URLs and watch the Page indexing report. Repeated requests without a change to the page do not solve the cause.
Related help
Sources for technical rules
Google's documentation is the authority for its own search systems. This guide explains the work in our words.