Webpage Registration & Payment Integration

I have a single HTML page— https://xpertus.com/seminardmk60.html —built with ChatGPT. I now need a lightweight registration flow added:

• A visitor chooses a seminar date, pays a flat $5 fee, and submits a short form. I’m open to either Stripe or PayPal—pick whichever lets you wire things up fastest.
• Form data (name, email, phone at minimum) should land in a Google Sheet in real time.
• Immediately after payment, the student receives a branded confirmation email; later, I can tweak that message myself.

Please embed clean, commented code so I can edit dates, fees, and email copy without touching anything complicated. A short README or inline comments are fine—no huge documentation set required.

The page is static, so if you plan to use Apps Script, PHP, Node, or another lightweight backend, host it somewhere simple or show me how to deploy it on my own domain. This is a quick task; once the flow works end-to-end and data appears in the spreadsheet, the job is done.