Ruby on Rails

This model has some errors that I wasn't able to get sorted out the two lines that begin with validate should be validates but after that I don't understand what the author's trying to do If I change them to validates I get the error Unknown validator: 'MessageValidator' for   validate :auction_active?, message: :auction_active

class Bid < ActiveRecord::Base

  belongs_to :auction

  belongs_to :user

  validates :auction, :user, presence: true

  validate :auction_active?, message: :auction_active

  validate :last_user_different?

  scope :sorted, -> { order(:created_at) }

  after_create :update_auction

  private

  def auction_active?

    if auction && !auction.active?

      if auction.finished?

        errors.add(:auction, :finished)

      else

        errors.add(:auction, :not_started)

      end

    end

  end

  def last_user_different?

    if auction && user

      errors.add(:user, :same_user_twice) if auction.last_user == user

    end

  end

  def update_auction

    auction.increase_price_and_time

    auction.publish_updates

  end

end