Problems installing Docker Extension

Hi,

I have problems installing the Plesk docker extension on a Ubuntu 16.04 LTS. Trying to install the extensions ends in following error:

plesk installer --select-release-current --install-component docker:


Checking whether the package dependencies are resolved.

Installing packages


ERROR: Failed to install or upgrade the extension 'Docker' (package: docker):
The extension docker is not allowed for installation.


Warning! Not all packages were installed.
Please check if your system...

Problems installing Docker Extension