How to Fix Cloudflare 521 Error with Firewall Settings - DNS Probe Finished NXDOMAIN: Quick Fixes-Diagnosing Cloudflare 522 Errors Using Server Logs
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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