Websites that have a shopping cart or checkout page, either using a known ecommerce platform or a custom solution.
Google Tag Manager is a tag management system (TMS) that allows you to quickly and easily update measurement codes and related code fragments collectively known as tags on your website or mobile app.
reCAPTCHA is a free service from Google that helps protect websites from spam and abuse.
A modest JavaScript framework for the HTML you already have.
WhatsApp Business is a free to download app available on Android and iPhone using which businesses can connect with their customers.