add paper trail

app/controllers/admin/application_controller.rb

@@ -2,5 +2,12 @@
 module Admin
   class ApplicationController < Administrate::ApplicationController
     before_action :authenticate_admin_user!
+    before_action :set_paper_trail_whodunnit
+
+    # used by #set_paper_trail_whodunnit
+    def current_user
+      # add admin prefix to differentiate from a customer
+      "admin/#{current_admin_user.id}"
+    end
   end
 end

app/controllers/application_controller.rb

@@ -1,5 +1,6 @@
 # frozen_string_literal: true
 class ApplicationController < ActionController::Base
+  before_action :set_paper_trail_whodunnit
   before_action :configure_devise_permitted_parameters, if: :devise_controller?
 
   protected

app/models/balance.rb

@@ -22,6 +22,8 @@
 #  fk_rails_...  (user_id => users.id)
 #
 class Balance < ApplicationRecord
+  include Trackable
+
   belongs_to :user
   belongs_to :currency
 

app/models/concerns/trackable.rb

@@ -0,0 +1,8 @@
+# frozen_string_literal: true
+module Trackable
+  extend ActiveSupport::Concern
+
+  included do
+    has_paper_trail
+  end
+end

app/models/fiat_balance.rb

@@ -20,6 +20,8 @@
 #  fk_rails_...  (user_id => users.id)
 #
 class FiatBalance < ApplicationRecord
+  include Trackable
+
   belongs_to :user
 
   monetize :amount_cents