530 Site is frozen / Origin Unavailable
Meaning
A non-standard status code with different meanings depending on context: Pantheon hosting uses 530 to indicate a site has been frozen (usually for inactivity or billing issues), while Cloudflare/Shopify have used 530 when the origin host is unreachable (for instance, DNS failure or other origin errors).
When to Use
Pantheon: use 530 when a site is taken offline or "frozen" due to inactivity or account issues. Cloudflare/Shopify: use 530 as an error when the origin cannot be reached at all (similar to a DNS or routing error that prevents connecting to the origin).
Example
Pantheon’s platform might return 530 Site is frozen if a website has been archived due to the user not upgrading or it being idle. In a DNS context, Cloudflare may also return a 530 if it cannot resolve the origin's DNS or otherwise finds the origin unavailable, although Cloudflare more commonly uses 523 or other codes for similar situations.
When Not to Use
Do not use in standard HTTP situations, as 530 is not officially defined. These are very specific uses: Pantheon’s internal handling or Cloudflare/Shopify's error signaling. Use standard codes (such as 503 or 523) for general cases of site unavailability or DNS issues in your own systems.
Source
Unofficial (Pantheon / Cloudflare / Shopify)