Integrate PayPal V6 Checkout

I have a small, custom-built JavaScript shopping cart that serves only digital downloads. At the moment it relies on a single PayPal “Pay Now” button; every product click jumps straight to payment. I’m ready to switch to PayPal’s newer V6 Checkout so customers can add several items, review a summary, and then pay—while still receiving instant download links on successful payment.

The cart logic, product data, and fulfilment scripts are already in place; what’s missing is the payment layer. Your job is to:

• Replace the legacy button with the PayPal V6 JavaScript SDK checkout flow (client-side plus the minimal server-side validation it requires).
• Preserve my existing download-delivery routine: once PayPal confirms payment, the customer should immediately receive the secure file link exactly as they do now.
• Keep the front-end experience lightweight—vanilla JavaScript is preferred so I don’t add a framework overhead.
• Leave clear, well-commented code so I can maintain future product additions myself.

If you’ve previously migrated custom carts to the PayPal V6 SDK, that experience will help us move quickly. Let me know roughly how long you’ll need and what access or sandbox credentials you require, and we can get started right away.