Error: Process is not alive while implementing a Stack through genserver

Hello everyone,

I am implementing a stack with Genserver, but I keep getting an error saying there is no process alive. Please go through the code below.

defmodule Stack.Server do
  use GenServer

  def start(_elements) do
      IO.puts "Hello"
      GenServer.start_link(__MODULE__, [4,5,"cool"])
    end

  def init(init_num) do
    {:ok, init_num}
  end


  def handle_call( _from,:pop,[h|t]) do
    IO.inspect [h|t]
    IO.inspect [t]
    IO.puts "handling call"
    {:reply, {:ok,h}, t}
  end

  def handle_cast({:push,value},state) do
    IO.inspect value
    IO.puts "handling cast"
    {:reply, {:ok,value}, [value|state]}
  end

  def pop(pid) do
      IO.puts "Inside popping stack"
      IO.inspect pid
       GenServer.call(:pops, pid)
   end

   def push(stack, item) do
     IO.puts "Inside pushing stack"
     GenServer.cast(stack,{:push,item})
   end

end

{:ok, pid} = Stack.Server.start [1,2,3]
Stack.Server.pop(pid)
Stack.Server.push(pid, 10)
Stack.Server.pop(pid)

And the error message says:

Compiling 2 files (.ex)
Hello
Inside popping stack
#PID<0.121.0>

== Compilation error in file lib/stack/server.ex ==
** (exit) exited in: GenServer.call(:pops, #PID<0.121.0>, 5000)
    ** (EXIT) no process: the process is not alive or there's no process currently associated with the given name, possibly because its application isn't started
    (elixir) lib/gen_server.ex:999: GenServer.call/3

Thanks a lot in advance
PS: I am a beginner.