Create a MercadoPago Preference when a document is created in Firestore

firebase-function-mercadopago.js

const functions = require('firebase-functions');
const admin = require('firebase-admin');
let FieldValue = require('firebase-admin').firestore.FieldValue;

admin.initializeApp();

const db = admin.firestore();
const express = require('express');
const app = express();
const mercadopago = require('mercadopago');

// WARNING: You need to use the Pay As You Go plan to use this function
mercadopago.configure({
    sandbox: true,
    access_token: '<YOUT ACCESS TOKEN>'
});

exports.createPreferenceForOrder = functions.firestore
    .document('orders/{orderId}')
    .onCreate(async (snap, context) =>  {
      const data = snap.data();
      let preference = {
          items: [
              {
                  title: data.name,
                  quantity: 1,
                  currency_id: 'ARS',
                  unit_price: data.price
              }
          ],
          payer: {
              email: "demo@gmail.com"
          }
      };

      let response = await mercadopago.preferences.create(preference);
      let preferenceId = response.body.id;

      snap.ref.set({"preference_id": preferenceId}, {merge: true});
    });