Fix 'Port Already Used by Another Container' in Docker Compose - How to Fix Cloudflare 521 Error with Wildcard Subdomains-Troubleshooting Docker 'network not found' and 'permission denied'

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.