Symptoms
Unable to upload a backup created on another server to Tools & Settings > Backup Manager:
Error: Unable to upload backup.zip to the server storage: Unable to import file as dump: Import error: Unable to find archive metadata. The archive is not valid Plesk backup or has been created in an unsupported Plesk version
Cause
The backup was created on Plesk for Linux and is uploaded to Plesk for Windows or vice-versa.
The following fragment from backup_info_xxx.xml file confirms it's from a Linux instance:
<migration-dump agent-name="Plesk.PHP" dump-version="18.0.41" dump-original-version="18.0.41" content-included="true" dump-format="panel" encryption-type="none">
<dump-info>
<description>All configuration and content</description>
<os-description type="unix" apache-uid="48" apache-gid="48" mailman-uid="41" mailman-gid="41"/>
...
This feature is not supported at the moment because the backup structure on Linux and on Windows is different.
Resolution
Use the Site Import extension to transfer the content from one server to another.