"554 Please activate your Mailgun account. Check your inbox or log in to your control panel to resend the activation email." error Ruby on Rails

I am building a web app using Ruby on Rails. I am using Mailgun as my mailer for this app. when i sign up using Facebook it works fine but when i try to sign up using email and password , i keep getting this error "554 Please activate your Mailgun account. Check your inbox or log in to your control panel to resend the activation email." I have already authorized the eamil to the Authorized Recipients in mailgun dashboard. Here's my code:

Registrations_controller.rb

class RegistrationsController < Devise::RegistrationsController
  protected
    def update_resource(resource,params)
      resource.update_without_password(params)
    end
end

config/environments/development.rb

 Rails.application.configure do
  # Settings specified here will take precedence over those in config/application.rb.

  # In the development environment your application's code is reloaded on
  # every request. This slows down response time but is perfect for development
  # since you don't have to restart the web server when you make code changes.
  config.cache_classes = false

  # Do not eager load code on boot.
  config.eager_load = false

  # Show full error reports.
  config.consider_all_requests_local = true

  # Enable/disable caching. By default caching is disabled.
  if Rails.root.join('tmp/caching-dev.txt').exist?
    config.action_controller.perform_caching = true

    config.cache_store = :memory_store
    config.public_file_server.headers = {
      'Cache-Control' => 'public, max-age=172800'
    }
  else
    config.action_controller.perform_caching = false

    config.cache_store = :null_store
  end

  # Don't care if the mailer can't send.
  config.action_mailer.raise_delivery_errors = true

  config.action_mailer.perform_caching = false

  # Print deprecation notices to the Rails logger.
  config.active_support.deprecation = :log

  # Raise an error on page load if there are pending migrations.
  config.active_record.migration_error = :page_load

  # Debug mode disables concatenation and preprocessing of assets.
  # This option may cause significant delays in view rendering with a large
  # number of complex assets.
  config.assets.debug = true

  # Suppress logger output for asset requests.
  config.assets.quiet = true

  # Raises error for missing translations
  # config.action_view.raise_on_missing_translations = true

  # Use an evented file watcher to asynchronously detect changes in source code,
  # routes, locales, etc. This feature depends on the listen gem.
  config.file_watcher = ActiveSupport::EventedFileUpdateChecker

  config.action_mailer.default_url_options = { host: 'localhost', port: 3000 }

  config.action_mailer.delivery_method = :smtp
  config.action_mailer.smtp_settings = {
  address: 'smtp.mailgun.org',
  port: 587,
  domain: 'sandboxc77c3a9be90a494081dad1628d554337.mailgun.org',
  authentication: 'plain',
  user_name: 'postmaster@sandboxc77c3a9be90a494081dad1628d554337.mailgun.org',
  password: 'password'
}


end

initalizers/devise.rb

      # If true, requires any email changes to be confirmed (exactly the same way as

      config.reconfirmable = false

  config.mailer_sender = 'ahmed @ iGloo <no-reply@igloo.com>'

views/devise/registrations/new.html.erb

<div class="row">
  <div class="col-md-4 col-md-offset-4">
<h2>Sign up</h2>

<%= form_for(resource, as: resource_name, url: registration_path(resource_name)) do |f| %>
  <%= render 'layouts/shared/devisemes' %>

    <div class="form-group">
    <%= f.text_field :fullname, autofocus: true , placeholder: "Full Name" , class: "form-control" %>
  </div>

  <div class="form-group">
    <%= f.email_field :email, autofocus: true , placeholder: "Email" , class: "form-control" %>
  </div>

  <div class="form-group">
    <%= f.label :password %>
    <% if @minimum_password_length %>
    <em>(<%= @minimum_password_length %> characters minimum)</em>
    <% end %><br />
    <%= f.password_field :password, autocomplete: "off" , placeholder: "Password" , class: "form-control" %>
  </div>



  <div class="actions">
    <%= f.submit "Sign up" , class: "btn btn-normal btn-block" %>
  </div>
<% end %>

<%= link_to "Sign up with Facebook", user_facebook_omniauth_authorize_path , class: "btn btn-facebook btn-block"%>


<%= render "devise/shared/links" %>
</div>
</div>