In general, the book isn’t yet updated for Phoenix version 1.6. On page 18 of the book, the authors indicate that an auto generated of router.ex should contain:

scope "/", PentoWeb do
    pipe_through :browser
    live "/", PageLive, :index
end

This code is no longer generated. Specifically, the line:

live "/", PageLive, :index

This is troubling since this occurs in the “Getting to Know LiveView” section, the very section that should be easy to understand for first time users.