HELP! Rest API - AddVisual

[ChippyDan]

OK - this is frustrating me to no end.  I am trying to mock up a simple example and I keep running into "is undefined" issues.
I am trying to take the example of adding a visual field to a "table" and it keeps saying that "SetAuthorizingPageActive" is not a function.  Where is this function?  Am I missing a library?

I'm developing with C# and VueJS - Someone save my sanity LOL.