Docs are confusing right now. There are two guides named “Installing an External Smart Proxy Server 3.3”, one for katello (proxy including content) and one for foreman only (proxy with no content).
Foreman: Installing an External Smart Proxy Server 3.3
Katello: Installing an External Smart Proxy Server 3.3
You are mixing them which does not work.
You should first decide what you want: do you need a proxy with content gateway or not? Currently, this defines the scenario you have to use, i.e. you cannot really switch after you have installed it.
The katello foreman-proxy-scenario should work well following the docs,
The foreman scenario, however, has some issues which I am fighting with at the moment. It needs some manual work to get the necessary certificates. See my topic Foreman-installer scenario for foreman-proxy installation