On the Linux Plesk Server if you find any of the domain suspended and while trying activate it you get error as below

Warning: The domain is still suspended for the following reason: Domain is temporarily suspended for backing up or restoring.

You may check the Backup Settings, this you can be found at

1. Domains -> Your Domain -> Backup Manager -> Scheduled Backup Settings

2. Uncheck the option to  Suspend domain until backup task is completed

4. Click “OK”.

Now to unsuspend the domain login to the server using SSH as root user and execute the following command

/usr/local/psa/bin/domain -u yourdomain -status enabled