There may come a time, when you are updating WordPress, either updating the main core or one of the plugins, and you get stuck with a “Briefly unavailable for scheduled maintenance. Check back in a minute” message. Here I’ll show an easy fix you can use with your FTP program.
Run Home Screaming! No, just kidding if this option is not working for you and you were updating some WordPress Plugins, then you can try to manually download the plugins that were involved with the update, then upload them via FTP. If there was an underlying issue with one of those plugins getting installed via the WordPress system, then uploading them via FTP should be the next option to try.