Message is not sent from external module

I am trying to send a message to Slack and I have a separate module to do that:

defmodule Slack.MessagePoster do
  @slack_bot Slack.Bot
  @slack_api_key "API_KEY"

  def send_message!(channel, message) do
    {:ok, rtm} = @slack_bot.start_link(Slack.MyRtm, [], @slack_api_key)
    {:message, _, _} = send(rtm, {:message, message, channel})
  end
end

And I call it as (inside iex -S mix)

MyRtm looks like this:

defmodule Slack.MyRtm do
  use Slack

  def handle_connect(slack, state) do
    IO.puts "Connected as #{slack.me.name}"
    {:ok, state}
  end

  def handle_event(_, _, state), do: {:ok, state}

  def handle_info({:message, text, channel}, slack, state) do
    IO.puts "Sending message, text: #{text}, channel: #{channel}"
    send_message(text, channel, slack)

    {:ok, state}
  end
  def handle_info(_, _, state), do: {:ok, state}
end

Slack.MessagePoster.send_message!("#general", "Never mind me, I'm just a test message")

I get {:message, "Never mind me, I'm just a test message", "#general"} as a response, but nothing get posted to Slack. But, if just bypass my send_message!/2 call and call this directly

{:ok, rtm} = @slack_bot.start_link(Slack.MyRtm, [], @slack_api_key)
{:message, _, _} = send(rtm, {:message, message, channel})

Everything works as expected (I see message in the Slack). Do you know what might be the problem here?

BlakeWilliams / Elixir-Slack

Message is not sent from external module #166