omniauth: (facebook) Authentication failure! uninitialized constant Users: NameError, uninitialized constant Users

Question

I have been looking for the solution but couldn't got luck, tried multiple solutions too.. but yet stuck..

What I am trying to do is adding facebook login to my app.. I'll try to explain and share the code as much as possible.

ruby version: 2.6.6 rails: 6.0.3

Here is the Gemfile

gem 'omniauth', '~> 2.0', '>= 2.0.4'
gem 'omniauth-oauth2', '~> 1.7', '>= 1.7.2'
gem 'omniauth-facebook'
gem 'devise', '~> 4.8', '>= 4.8.1'
gem 'simple_token_authentication', '1.17.0'
gem 'devise-async', '1.0.0'
gem 'activeadmin', '~> 2.6', '>= 2.6.1'

the devise.rb file

config.omniauth :facebook, "APPID", "APPSECRET", callback_url: "http://localhost:3000/users/auth/facebook/callback"

here is my User Model

class User < ApplicationRecord
    devise :database_authenticatable, :registerable,
            :recoverable, :rememberable, :validatable,
            :trackable, :async,
            :omniauthable, :omniauth_providers => [:facebook]


    ## Token Authenticatable
    acts_as_token_authenticatable
    
    def devise_mailer
        UserMailer
    end

    def self.new_with_session(params, session)
        super.tap do |user|
        if data = session["devise.facebook_data"] && session["devise.facebook_data"]["extra"]["raw_info"]
            user.email = data["email"] if user.email.blank?
        end
        end
    end
    
    def self.from_omniauth(auth)
        where(provider: auth.provider, uid: auth.uid).first_or_create do |user|
        user.email = auth.info.email
        user.encrypted_password = Devise.friendly_token[0,20]
        user.first_name = auth.info.name   # assuming the user model has a name
        end
    end
end

in routes file

devise_for :users, controllers: { registrations: "api/v1/users/registrations", sessions: "api/v1/users/sessions", passwords:  "api/v1/users/passwords", omniauth_callbacks: "users/omniauth_callbacks" }

the omniauth controller app/controller/api/v1/users/omniauth_callbacks_controller.rb

# frozen_string_literal: true

class Api::V1::Users::OmniauthCallbacksController < Devise::OmniauthCallbacksController
    def facebook
        @user = User.from_omniauth(request.env["omniauth.auth"])

        if @user.persisted?
        sign_in_and_redirect @user, :event => :authentication
        set_flash_message(:notice, :success, :kind => "Facebook") if is_navigational_format?
        else
        session["devise.facebook_data"] = request.env["omniauth.auth"]
        redirect_to new_user_registration_url
        end
    end

    def failure
        redirect_to root_path
    end
end

and finally the link for social login link_to "Sign in with Facebook", user_facebook_omniauth_authorize_path, method: :post which is generating the URL http://localhost:3000/api/v1/users/auth/facebook

and when clicked, I get below error

Started POST "/api/v1/users/auth/facebook" for 172.19.0.1 at 2022-02-15 12:47:28 +0000
D, [2022-02-15T12:47:28.580549 #1] DEBUG -- omniauth: (facebook) Request phase initiated.
W, [2022-02-15T12:47:28.582705 #1]  WARN -- omniauth: Attack prevented by OmniAuth::AuthenticityTokenProtection
E, [2022-02-15T12:47:28.582960 #1] ERROR -- omniauth: (facebook) Authentication failure! authenticity_error: OmniAuth::AuthenticityError, Forbidden
E, [2022-02-15T12:47:28.591291 #1] ERROR -- omniauth: (facebook) Authentication failure! uninitialized constant Users: NameError, uninitialized constant Users

NameError (uninitialized constant Users):

activesupport (6.0.4.6) lib/active_support/inflector/methods.rb:282:in `const_get'
activesupport (6.0.4.6) lib/active_support/inflector/methods.rb:282:in `block in constantize'
activesupport (6.0.4.6) lib/active_support/inflector/methods.rb:280:in `each'
activesupport (6.0.4.6) lib/active_support/inflector/methods.rb:280:in `inject'
activesupport (6.0.4.6) lib/active_support/inflector/methods.rb:280:in `constantize'
devise (4.8.1) lib/devise/omniauth.rb:18:in `block in <main>'
omniauth (2.0.4) lib/omniauth/strategy.rb:544:in `fail!'
omniauth (2.0.4) lib/omniauth/strategy.rb:199:in `rescue in call!'
omniauth (2.0.4) lib/omniauth/strategy.rb:191:in `call!'
omniauth (2.0.4) lib/omniauth/strategy.rb:169:in `call'
warden (1.2.9) lib/warden/manager.rb:36:in `block in call'
warden (1.2.9) lib/warden/manager.rb:34:in `catch'
warden (1.2.9) lib/warden/manager.rb:34:in `call'
rack (2.2.3) lib/rack/tempfile_reaper.rb:15:in `call'
rack (2.2.3) lib/rack/etag.rb:27:in `call'
rack (2.2.3) lib/rack/conditional_get.rb:40:in `call'
rack (2.2.3) lib/rack/head.rb:12:in `call'

I have gone through many solutions shared on stackoverflow and github#issues but none worked for me.. If anyone can tell me what I am doing wrong here that'll be really great...

I have tried to share my code and explain the problem... but if incase I missed something, then please accept my apologies, I'll be happy to share any further information if missed or asked..

Thank you in advance..