not working superviser

gistfile1.ex

defmodule Lucas do
  use Application
  # Import helpers for defining supervisors
  import Supervisor.Spec

  def start(_type, _args) do
    IO.puts "starting"
    # This time, we don't pass any argument because
    # the argument will be given when we start the child
    children = [
      worker(Poller, [%{timeout: 1, update_id: 0}], restart: :transient)
    ]
    # Start the supervisor with our one child
    {:ok, sup_pid} = Supervisor.start_link(children, strategy: :simple_one_for_one)
    {:ok, pid} = Supervisor.start_child(sup_pid, [])
  end
end


defmodule Poller do
  use GenServer
  require Logger

  def start_link(state) do
    GenServer.start_link(__MODULE__, state)
  end

  def init(state) do
    IO.puts "Pooling server started"
    spawn fn ->
      handle_cast(:start_pool, state)
    end
    {:ok, state}
  end

  def handle_cast(:start_pool, state) do
    lol
    {:noreply, state}
  end

  def lol do
    throw("x")
  end
end