How to fix No route matches [GET] “/auth/shopify” after introducing devise with Omniauth?

devise.rb

# Commented the following line, moved it to omniauth.rb
# config.omniauth :google_oauth2, Settings.google.client_id, Settings.google.client_secret, { access_type: "offline", approval_prompt: "" }

omniauth.rb

Rails.application.config.middleware.use OmniAuth::Builder do
  provider :shopify,
    ShopifyApp.configuration.api_key,
    ShopifyApp.configuration.secret,
    scope: ShopifyApp.configuration.scope,
    callback_path: "#{Settings.shopify.mounted_at}/auth/shopify/callback"

  provider :google_oauth2,
           Settings.google.client_id,
           Settings.google.client_secret,
          { access_type: "offline", approval_prompt: "" }
end

routes.rb

devise_for :users #, controllers: { omniauth_callbacks: 'users/omniauth_callbacks' }
get '/auth/google_oauth2/callback' => 'users/omniauth_callbacks#google_oauth2'

user.rb

class User < ApplicationRecord
  devise :database_authenticatable, :rememberable, :trackable, :validatable #, :omniauthable
end