[Heroku] Receiving forbidden request when I don't set a fixie proxy and internal error if a set it as endpoint

[caherrerapa]

I'm trying to make it work using heroku. The message is received correctly but when I try to send a message back:

1. I get forbidden request if I don't set any endpoint
2. I get HTTPInternalServerError if I set to fixie http endpoint, but I'm not sure if this is correct. Really appreciate any help. Maybe @hirohisa can give some lights?

require 'line/bot'

class CallbacksController < ApplicationController
  def event_handler
    signature = request.env['HTTP_X_LINE_CHANNELSIGNATURE']
    unless client.validate_signature(request.body.read, signature)
      error 400 do 'Bad Request' end
    end

    receive_request = Line::Bot::Receive::Request.new(request.env)

    receive_request.data.each { |message|
      puts message.to_json
      case message.content

      when Line::Bot::Message::Text
         # All the code above works correctly this call is the problematic
         res = client.send_text(
          to_mid: message.from_mid,
          text: "Hola",
        )
        puts "#{res}"
        puts "#{client.endpoint}"
      end
    }

    render :nothing => true, status: :ok
  end

  def client
    client ||= Line::Bot::Client.new do |config|
      config.channel_id = ENV.fetch('LINE_CHANNEL_ID')
      config.channel_secret = ENV.fetch('LINE_CHANNEL_SECRET')
      config.channel_mid = ENV.fetch('LINE_CHANNEL_MID')
      # I get either 500 if set and forbidden if i remove this line
      config.endpoint = ENV.fetch('LINE_OUTBOUND_PROXY')
    end
  end
end

[caherrerapa]

Closing as the request class doesn't support proxy. My bad