index.js - (addRequestHandlers for purchases).js

const skillBuilder = Alexa.SkillBuilders.custom();
exports.handler = skillBuilder
  .addRequestHandlers(
    ...
    PurchaseHandlers.WhatCanIBuyIntentHandler, // purchase handlers
    PurchaseHandlers.TellMeMoreAboutProductIntentHandler,
    PurchaseHandlers.BuyIntentHandler,
    PurchaseHandlers.BuyResponseHandler,
    PurchaseHandlers.PurchaseHistoryIntentHandler,
    PurchaseHandlers.RefundProductIntentHandler,
    PurchaseHandlers.CancelProductResponseHandler,
    ...
  )
  .addRequestInterceptors(myLocalizationInterceptor, initPurchaseHandlers) // lang & purchase
  .addErrorHandlers(GlobalHandlers.ErrorHandler)
  .withApiClient(new Alexa.DefaultApiClient()) // API to get user permissions and in-skill purchases
  .lambda();