To send payment invoices and notifications to users via WhatsApp, you can use the Twilio API for WhatsApp, Stripe, Laravel, PHP, and other tools. You will need a Twilio account, Composer, Ngrok, and Laravel CLI installed on your machine, as well as knowledge of the Laravel framework and a Stripe account. To get started, create a new Laravel application and install the necessary dependencies using composer. Next, set up the database tables for users and products, seed them with sample data, and create the necessary models for products and users. You will also need to create views for the home page and checkout page, as well as a controller to handle application logic. The controller will use the Stripe API to charge the user's card and send a WhatsApp message with an invoice PDF attachment. Finally, set up routes for the application and start the server to test the functionality of sending payment invoices and notifications via WhatsApp.