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Cloudflare Wildcard Subdomain CNAME Setup Guide - How to Fix Cloudflare Error 521: Origin Server Unreachable-Fix npm run build Failure from Missing Env Variables

Updated 2026-07-28 14:43:30macos-help
Cloudflare Wildcard Subdomain CNAME Setup Guide - How to Fix Cloudflare Error 521: Origin Server Unreachable-Fix npm run build Failure from Missing Env Variables
Before changing system settings, save your work and note the exact error text so you can compare results after each step.

Extra verification checklist

  • Restart the affected app after changing permissions or configuration files.
  • Test the same workflow in a clean browser profile or a temporary user account.
  • Compare the result on another network if the error may be connection related.

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