Digital Checkout Integration Upgrade

I’m overhauling the checkout flow on my site, which sells only digital products such as downloads and license keys. The job is to build (or refactor) a single-page checkout that cleanly accepts both Credit/Debit Card payments and PayPal, then confirms the order and triggers the existing digital-delivery hook.

Key deliverables
• Seamless integration of Card and PayPal gateways, showing the correct option set based on the customer’s choice.
• Captcha verification on the payment step to reduce bot traffic without hurting conversion.
• Automatic redirect to my “thank-you / download” page once payment is approved, passing the order ID so my current download script can pick it up.
• Clear, commented code (PHP/JavaScript) that I can extend later and a brief read-me outlining where to update API keys.

Everything must run smoothly on the current stack (HTML5, CSS3, PHP 8, MySQL) with no framework lock-in. I’ll provide sandbox API keys for testing, and final acceptance happens once I’ve processed a live $0.01 test transaction on each gateway with captcha enabled.

If you’ve rolled out a similar digital-only checkout before, you should find this straightforward.