A failed check means the app could not confirm the sitemap URL. Your products and pages are still in Shopify.
Look at the storefront in a browser and open the sitemap URL Shopify uses. If that page errors, the task will report a problem too.
What to check
- Confirm the store is not password-protected in a way that blocks the sitemap
- Confirm the primary domain is the one you expect
- Read the problem count in History
- Run the task again after the sitemap responds
The llms.txt file can still publish when the sitemap check has a problem. They are separate results on the same task.