The Katello plugin required to manage content in Foreman is not supported for Foreman on Debian/Ubuntu.
With Foreman and Katello on Enterprise Linux, you can provide content to hosts running Debian/Ubuntu.
If you want to manage content using Foreman/Katello, you have to run Foreman/Katello on Enterprise Linux. Converting an existing Foreman installation on Enterprise Linux to Foreman/Katello is not supported. For more information, see Installing Foreman Server with Katello plugin on Enterprise Linux.