If you ever get the “is not a member of” error, it is simply stating that whatever you have typed doesn’t exist in the class you’re calling it from. So even if you think that you have spelled it correctly, or that it is there, if you get this error, it’s actually not.
You can always open the class and double check the functions that are included in it and its parent class(es) for what you are trying to use.
Furthermore, you can search the UE4 documentation here:
https://docs.unrealengine.com/latest/INT/
As an example, for AddToViewPort (spelled incorrectly):
https://docs.unrealengine.com/latest/INT/Search/index.html?q=AddToViewPort&x=0&y=0
If you select the “API” tab, you can then see its actually spelled as, AddToViewport( ):
Hope this helps.