If you want to back up databases hosted on a remote Microsoft SQL Server that you registered in Plesk earlier, you need to configure the database backup settings for that Microsoft SQL Server.
To configure backup settings for a remote Microsoft SQL Server:
This temporary physical directory is required for backing up and restoring remote SQL Server databases: SQL Server places temporary backup files in this directory during backup, and Plesk places temporary backup files in this directory during restoration. You must create this directory on the remote server and make it accessible by the MS SQL server to read and write.
The Plesk server will use this directory to download and upload the temporary backup files. You must create the network directory on the remote server, mount it to a temporary physical directory created in the previous step, and make it accessible over network by the user created in the next step.
ServerName\db_backup_user) and give this user read/write access to the temporary network directory.
The Plesk server will use this user to access the temporary directory.