Gibbon::MailChimpError (the server responded with status 400 @title="Invalid Resource"

I am trying to use gibbon gem and following their github docs. Here is the code I have

class ChimpController < ApplicationController
  def create
    send_to_mail_chimp ( params[:email])
  end

  def send_to_mail_chimp(email)
    puts "send email is #{email}"
    gibbon = Gibbon::Request.new(api_key: "bla")
    gibbon.timeout = 10
    gibbon.lists('e61cf2454d').members.create(body: {email_address: email, status: "subscribed"})
  end
end

<%= simple_form_for :email, url: newsletter_path, :method => :post do |f| %> <%= f.input :email, input_html: {class: 'form-control', placeholder: 'enter email'} %> <% end %>

The exact error message is

Gibbon::MailChimpError (the server responded with status 400 @title="Invalid Resource", @detail="The resource submitted could not be validated. For field-specific details, see the 'errors' array.", @body={"type"=>"http://developer.mailchimp.com/documentation/mailchimp/guides/error-glossary/", "title"=>"Invalid Resource", "status"=>400, "detail"=>"The resource submitted could not be validated. For field-specific details, see the 'errors' array.", "instance"=>"", "errors"=>[{"field"=>"email_address", "message"=>"Schema describes string, object found instead"}]}, @raw_body="{\"type\":\"http://developer.mailchimp.com/documentation/mailchimp/guides/error-glossary/\",\"title\":\"Invalid Resource\",\"status\":400,\"detail\":\"The resource submitted could not be validated. For field-specific details, see the 'errors' array.\",\"instance\":\"\",\"errors\":[{\"field\":\"email_address\",\"message\":\"Schema describes string, object found instead\"}]}", @status_code=400):
  app/controllers/chimp_controller.rb:10:in `send_to_mail_chimp'
  app/controllers/chimp_controller.rb:3:in `create'

The error message you're getting back is telling you exactly what the problem is:

{
    "field": "email_address",
    "message": "Schema describes string, object found instead"
}

You're passing the email in as a javascript object (ruby hash) instead of a string. All you need to pass is the raw email address.