Every app needs billing and nobody wants to build it twice. SparkPay gives you a hosted pricing page, Stripe checkout, PDF invoices and a type-safe kit for gating features by plan in your own code. It covers the commercial side too: coupons, referrals, win-back campaigns and tax-ready exports. An MCP server lets an AI assistant read and change plans and revenue. Runs on your own Stripe account. Free for one app up to $1,000 processed.