acts_as_taggable ダグ機能実装

challenge記事にタグを付けたいのですが、このようなエラーが出てしまいます。
どうしてでしょうか。
よろしくお願いします。

class Challenge < ApplicationRecord
  belongs_to :user

  acts_as_taggable

  validates :titile, presence: true, length: { maximum: 255 }
  validates :description, presence: true, length: { maximum: 255 }


end

class ChallengesController < ApplicationController
  before_action :require_user_logged_in
  before_action :correct_user, only: [:destroy]


  def index
    if logged_in?
      @user = current_user
      @challenge = current_user.challenges.build  # form_for 用
      @challenges = current_user.challenges.order('created_at DESC').page(params[:page])
    end
  end

  def new
    @challenge = Challenge.new
  end

  def create
    @challenge = current_user.challenges.build(challenge_params)
    if @challenge.save
      flash[:success] = 'メッセージを投稿しました。'
      redirect_to root_url
    else
      @challenges = current_user.challenges.order('created_at DESC').page(params[:page])
      flash.now[:danger] = 'メッセージの投稿に失敗しました。'
      render 'toppages/index'
    end
  end

  def destroy
    @challenge.destroy
    flash[:success] = 'メッセージを削除しました。'
    redirect_back(fallback_location: root_path)
  end


  private

  def challenge_params
    params.require(:challenge).permit(:titile, :description, :tag_list)
  end

  def correct_user
    @challenge = current_user.challenges.find_by(id: params[:id])
    unless @challenge
      redirect_to root_url
    end
  end
end

class UsersController < ApplicationController
  before_action :require_user_logged_in, only: [:index, :show]

  def index
    @users = User.all.page(params[:page])

  end

  def show
    if logged_in?
      @user = current_user
      @challenge = current_user.challenges.build  # form_for 用
      @challenges = current_user.challenges.order('created_at DESC').page(params[:page])
    end

    @user = User.find(params[:id])
    @challenges = @user.challenges.order('created_at DESC').page(params[:page])
    counts(@user)
  end

  def new
    @user = User.new
  end

  def create
    @user = User.new(user_params)

    if @user.save
      flash[:success] = 'ユーザーを登録しました'
      redirect_to @user
    else
      flash.now[:danger] = '登録に失敗しました'
      render :new
    end
  end

  private

  def user_params
    params.require(:user).permit(:name, :email, :password, :password_confirmation)
  end
end

<div class="field form-group form-group-lg">
  <%= f.label :tag_list, class: "sr-only control-label" %>
  <%= text_field_tag 'draft[tag_list]', draft.tag_list.join(","), class: "form-control" %>
</div>

<%= form_for(@challenge) do |f| %>
        <div class="form-group">
          <%= f.text_area :titile, class: 'form-control', rows: 1 %>
          <%= f.text_area :description, class: 'form-control', rows: 5 %>
        </div>
        <%= f.submit 'Post', class: 'btn btn-primary btn-block' %>
<% end %>