Soft 404
A page that returns HTTP status 200 OK but actually shows error content — "currently unavailable," "out of stock," or similar. Looks healthy to status-code checkers; doesn't convert for buyers.
A "hard" 404 returns HTTP status 404 — the standard signal that a page doesn't exist. Easy to detect, easy to fix. A "soft" 404 returns status 200 OK — meaning the page technically exists and rendered — while the rendered content tells the user the product is unavailable, the listing has been removed, or the inventory has zeroed out.
Soft 404s are the most common silent affiliate-link failure. Amazon, Coolblue, Bol.com, and many others render "currently unavailable" pages with 200 OK status. Generic uptime checkers report the link as healthy because the status code passes. The only way to detect a soft 404 is to read the actual rendered content of the page — which is why specialized affiliate-link monitoring tools use AI page-reading rather than status checks alone.