You're looking at the latest documentation, not the documentation as it relates to the version you are running.
Take a look at this page - Versions-Tableau Server REST API
It notes you are using version 2.0 of the API with a schema version of 2.0.
There's a number of different reference pages available depending on your version, see this page - Reference-Tableau Server REST API
You're going to need to look at the REST API for Tableau Server 9.0 documentation. Even then, be careful to make sure you reference features of 2.0 only, not 2.0.1