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How to Fix Cloudflare Error 521: Web Server Is Down - Setting Up Cloudflare Wildcard Subdomains for Multiple Sites-Fix Chrome Certificate Error: Invalid Authority SSL Certificate

Updated 2026-07-28 17:41:00developer-tools

How to Fix Cloudflare Error 521: Web Server Is Down - Setting Up Cloudflare Wildcard Subdomains for Multiple Sites-Fix Chrome Certificate Error: Invalid Authority SSL Certificate

Prepare

Execute

Validate

Document

Operational follow-up

Record the exact option, command, or setting that changed the result.
Keep a rollback note if the workflow affects shared files or team settings.

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