parallels_installer_Debian_9.4_x86_64.md5sum was not found

Hi,

I've upgraded an existent server from Debian 8 to 9.4, everything works with the installed Plesk 12, now i'm trying to upgrade Plesk to the last version, but from the gui and the cli i get this error:

Unable to obtain the latest version of Plesk Installer: The required version '3.18.12' was not found on the server.
This could happen because of configuration error at the download site.
Failed to download the package...

parallels_installer_Debian_9.4_x86_64.md5sum was not found