Hubspot custom workflow function to send transactional email with custom data

custom.js

const hubspot = require('@hubspot/api-client');

exports.main = async (event, callback) => {
    // initialize the hubspot api client with your api secret
    const hubspotClient = new hubspot.Client({
        apiKey: process.env.API_KEY
    });

    // the ID of the email template
    const EMAIL_TEMPLATE_ID = 82546305923;

    // the ID of the current contact in the workflow
    const contactId = event.object.objectId;
    let contact = undefined;

    // Get contact details
    try {
        // set properties you want to fetch
        const properties = ["email", "firstname", "lastname"];
        const paginateAssociations = undefined;
        const associations = undefined;
        const archived = false;
        const api = hubspotClient.crm.contacts.basicApi;

        const apiResponse = await api.getById(contactId,
            properties,
            associations,
            paginateAssociations,
            archived);
        contact = apiResponse.body;
    } catch (e) {
        e.message === 'HTTP request failed'
            ? console.error(JSON.stringify(e.response, null, 2))
            : console.error(e)
        throw e;
    }

    // OUT OF SCOPE
    // Fetch some external data you want to render in your email template. In our
    // example we use a fixed HTML string for simplicity.
    const readingStats = "<tr><td>1</td><td>Hubspot Emails with Custom Data</td><td>1.200</td></tr>"

    // Send email with custom data
    try {
        // create send id to avoid multiple email sends for a customer on the same day
        const today = new Date().setHours(0, 0, 0, 0).toString();
        const sendId = "sendId_" + contact.id + "_" + today;

        // fill out the basic message properties
        const message = {
            "to": contact.properties.email,
            "sendId": sendId,
            "replyTo": [],
            "cc": [],
            "bcc": []
        };

        // set the contact properties
        const contactProperties = contact.properties;

        // here you can add all your custom data
        const customProperties = {
            readingStats: readingStats
        };

        // the final email message object
        const PublicSingleSendRequestEgg = {
            message,
            contactProperties,
            customProperties,
            emailId: EMAIL_TEMPLATE_ID
        };

        const api = hubspotClient.marketing.transactional.defaultApi;
        const apiResponse = await api.sendEmail(PublicSingleSendRequestEgg)
        console.log(JSON.stringify(apiResponse.body, null, 2));
    } catch (e) {
        e.message === 'HTTP request failed'
            ? console.error(JSON.stringify(e.response, null, 2))
            : console.error(e)
        throw e;
    }

    callback({outputFields: {}}); // call final callback without any parameters
}