Two main causes

1. Missing OG tags – og:title and friends aren’t in the server-rendered HTML
2. Admin-disabled previews – your Google Workspace administrator turned off link previews for the org

Diagnosis checklist

1. Check for OG tags – curl your URL and verify og:title is in the HTML (not JavaScript-injected).
2. Check HTTP status – must return 200 OK.
3. Check HTTPS – valid certificate required.
4. Check server-side rendering – client-side-only meta tags won’t be visible to the fetcher.
5. Check admin settings – ask your Workspace admin if previews are enabled.
6. Check firewall rules – don’t block requests from *.gae.googleusercontent.com.

robots.txt is irrelevant here

Google Chat’s fetcher ignores robots.txt – it’s classified as user-triggered. If previews aren’t showing, robots.txt isn’t the problem.

Testing your fix

curl -A "Google-Chat-Preview" https://yoursite.com/page | grep -i "og:title"

Then share the URL in a new Google Chat message to verify.