PayU Custom Payment Page

I’m building a standalone, minimalistic payment page that talks directly to PayU’s payment-processing API. The flow is deliberately simple: shoppers land on the page, pick Digital Wallet or UPI, complete the charge, and see an immediate success or failure message—no login or account creation anywhere in the journey.

Here’s the scope as I see it:

• API integration: generate the transaction hash, post to PayU, handle success / failure callbacks, verify the hash on return, and log the response securely.
• Payment methods: enable Digital Wallets and UPI only; card or net-banking options shouldn’t appear in the UI.
• UI/UX: clean, lightweight layout—think a single white panel, brand colors, and just the essential form elements. It must be mobile-first, responsive, and WCAG-friendly.
• Security: server-side key/secret storage, HTTPS enforcement, CSRF protection, and clear error handling.
• Deliverables: production-ready source code, brief setup notes, and a quick walk-through so I can plug in my own PayU keys and go live.

Feel free to propose the stack you’re most comfortable with (plain HTML/CSS/JS, React, Vue, etc.) as long as it keeps the page snappy and easy for me to maintain.