undefined local variable or method `acts_as_messageable'

[atulbishtZig]

The error arises when User model is configured with Mailboxer gem and it say's acts_as_messageable is undefined.
I tried to add acts_as_messageable method inside module PolicyManager::Concerns::UserBehavior
but still error shows up.
In model user.rb:

class User < ApplicationRecord
 
  # Include default devise modules.
  devise :database_authenticatable, :registerable,
          :recoverable, :rememberable, :trackable, :validatable,
          :confirmable   #, :omniauthable  #,:token_authenticatable
  include DeviseTokenAuth::Concerns::User
  
  include PolicyManager::Concerns::UserBehavior  #policy management
  
  acts_as_messageable
end

In gem PolicyManager::Concerns::UserBehavior

module PolicyManager::Concerns::UserBehavior
  extend ActiveSupport::Concern
  module ActiveRecordExtension
    def acts_as_messageable
   #code
    end
  end