Ruby on Rails - delegate devise member on has_and_belongs_to_many association

I have a has_and_belongs_to_many association between keywords and groups and then a groups belongs_to member association between group and devise.

class Keyword < ActiveRecord::Base
  has_and_belongs_to_many :groups
  delegate :member, to: :groups
  validate :keywords_within_limit, on: :create

  def keywords_within_limit
    if self.member.keywords(:reload).count >= self.member.keyword_limit
       errors.add(:keyword, "exceeded limit")
    end
  end
end

Im trying access my members methods using delegate but I am getting the error NoMethodError - undefined method member for #<ActiveRecord::Associations::CollectionProxy []>:

Why can't I access my members methods using delegate?