Error, “Briefly unavailable for scheduled maintenance. Check back in a minute” occurred while browsing your WordPress website. After a few minutes (> 5 minutes), the error still showing.
The WordPress upgrade is running
1. Wait a few minutes until the WordPress upgrade process is complete
2. Rerun your WordPress upgrade
3. Go to your root directory (via FTP or File Manager), find and delete .maintenance file. This is hidden file. After delete, please run the upgrade again.