HTML/CSS/JS Payment Integration

I already have a front-end project running and it’s time to add a fast, secure payment flow built purely with HTML, CSS and vanilla JavaScript—no frameworks.

Here’s what I need:
• A fully responsive checkout page that blends with my existing layout.
• Solid client-side validation and error handling.
• Hand-off to the payment gateway of our choice (we can finalise PayPal, Stripe or another option together) using the provider’s latest REST or JavaScript SDK.
• Clear, well-commented code plus a short read-me so I can maintain the integration later.

I’ll give you access to a test environment and the live keys once we’re satisfied in sandbox mode. Success is a seamless transaction from form submission through to the provider’s confirmation page, with no console errors and a clean return path to the site.

If you’ve done lightweight, front-end-only payment work before, let’s keep this simple and ship quickly.