PayPal Reference Transaction prototype, using implementation option 2 from https://developer.paypal.com/docs/archive/express-checkout/ec-set-up-reference-transactions/#implementation-options

paypal-checkout-reference-transactions.js

const fetch = require("node-fetch");
const config = {
  paypal: require("./paypal-config")["DEV"],
};

const PAYPAL_SANDBOX_NVP_BASE_URL = "https://api-3t.sandbox.paypal.com/nvp";
const nvpUrl = new URL(PAYPAL_SANDBOX_NVP_BASE_URL);
const params = {
  USER: config.paypal.USER, // Merchant username
  PWD: config.paypal.PWD, // Merchant password
  SIGNATURE: config.paypal.SIGNATURE, // Merchant signature
  METHOD: "SetExpressCheckout",
  VERSION: 204, // TODO: Finalize version
  PAYMENTREQUEST_0_PAYMENTACTION: "AUTHORIZATION",
  PAYMENTREQUEST_0_AMT: 0, // The amount authorized
  PAYMENTREQUEST_0_CURRENCYCODE: "USD", // The currency, e.g. US dollars
  L_BILLINGTYPE0: "MerchantInitiatedBilling", // The type of billing agreement
  L_BILLINGAGREEMENTDESCRIPTION0: "TestAuthorization", // The description of the billing agreement
  cancelUrl: "https://example.com/cancel", // For use if the consumer decides not to proceed with payment
  returnUrl: "https://example.com/success", // For use if the consumer proceeds with payment
};
Object.keys(params).forEach(key => nvpUrl.searchParams.append(key, params[key]));

async function setupPaymentAuthorization() {
  const metadata = {
    method: "POST",
    body: nvpUrl.searchParams.toString(),
  }
  const response = await fetch(PAYPAL_SANDBOX_NVP_BASE_URL, metadata);
  if (!response.ok) {
    throw new Error(`${response.statusText}`);
  }
  const data = await response.text();
  console.log(data);
  // A successful response is logged of the form described at https://developer.paypal.com/docs/archive/express-checkout/ec-set-up-reference-transactions/#response
}

// Step 1: Set up the payment authorization
setupPaymentAuthorization();
// TODO: Step 2: Redirect the buyer to PayPal for authorization.
// TODO: Step 3: Create the billing agreement to obtain the billing ID number.
// TODO: Step 4: Capture future payments.