Using runscope with mailgun - where to start?

Question

I've set up rails application to receive mails and create bookmarks from. Herefore I included the gem 'mailgun'. Because its not working correctly however I want to use runscope to get a better insight on which data is sent.

I've done the following steps in my application: 1. Added mailgun to heroku 2. Set up an initializer

ActionMailer::Base.smtp_settings = {
 port:              587, 
 address:           'smtp.mailgun.org',
 user_name:         ENV['MAILGUN_SMTP_LOGIN'],
 password:          ENV['MAILGUN_SMTP_PASSWORD'],
 domain:            'appurlhere.com',
 authentication:    :plain,
 content_type:      'text/html' 
}
ActionMailer::Base.delivery_method = :smtp

# Makes debugging *way* easier. 
ActionMailer::Base.raise_delivery_errors = true

3. Set up a route for incoming

   post :incoming, to: 'incoming#create'

4. Created the incoming controller

   def create
    @user = User.find_by_email(params[:sender])
    @topic = @user.topics.find_by(title: params[:subject])
    @url = "http://#{params["body-plain"]}"
   
    @user = User.create(email: params[:sender], password: "#{params[:subject]}") if @user.nil?
    @topic = Topic.create(title: params[:subject], user_id: @user.id) if @topic.nil?
    @bookmark = Bookmark.create(topic_id: @topic, user_id: @user, url: "what should be here")
    head 200
   end
   

But now I don't get where I should adjust code so I can see better data (and debug) better. I tried adding code to my routes in mailgun but that didn't work.