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... (Budget: $10 - $30 USD, Jobs: Google Sheets, HTML, JavaScript, MySQL, PayPal, PHP, Stripe, Web Development)