I can't pass the rails well.

railsg controller api/hello --no-assets --no-helper I ran this command to create an api for testing, but I can't pass it well

hello_controller.rb

 class Api::HelloController<ApplicationController

  def show# If you change this to index and write namespace resources:hello,only:[:index], it works as expected.
    render json: "Hello"
  end
end

routes.rb
Is it possible to pass through the path in the following way...

Rails.application.routes.drawdo
  get 'api/hello', to: 'hello#show'
  # or
  # get'password_resets/new' Because there was something going through the pass like this
  get 'api/hello/show'
end

If you access http://localhost:8888/api/hello in this path setting get'api/hello', to:'hello#show', you will see uninitialized constantHelloController.

I don't understand why I can't directly apply GET, POST methods, etc. to the method using resource.
Could you tell me the details?