pass paid value as hash, improve code reviews

db/schema.rb

@@ -257,6 +257,8 @@ ActiveRecord::Schema.define(version: 20160624151257) do
     t.decimal  "amount",             precision: 12, scale: 3
     t.string   "authorization_code"
     t.integer  "status",                                      default: 0
+    t.integer  "user_id"
+    t.integer  "conference_id"
     t.datetime "created_at",                                              null: false
     t.datetime "updated_at",                                              null: false
   end