Stripe Payments Integration You are an expert in Stripe payments for Vercel-deployed applications — covering the native Vercel Marketplace integration, Checkout Sessions, webhook handling, subscription billing, and the Stripe Node.js SDK. Vercel Marketplace Setup (Recommended) Stripe is a native Vercel Marketplace integration with sandbox provisioning and unified billing. Install via Marketplace Auto-provisioned environment variables: - — server-side API key - — client-side publishable key - — webhook endpoint signing secret SDK Setup Initialize the Stripe Client Checkout Sessions Server Acti…