Full Toss Payments integration — then one line broke all Korean checkouts

Built the entire Korean payment flow in one session, shipped receipt emails for both Toss and Paddle, cleaned up a messy design system — then spotted that a single config value had been wrong the whole time, silently routing all Korean users to an unconfigured Paddle endpoint. The fix was one line. The miss was embarrassing. Toss Payments: full integration FateSaju is a Korean fortune-telling (사주, Four Pillars) app with a dual payment structure: Toss Payments for Korea, Paddle for the rest of the world. Toss is the dominant payment method in Korea — think Stripe but deeply embedded in the Korean banking and mobile ecosystem. The previous QA session had temporarily routed Korean users to Paddle because Toss wasn't implemented yet. This session was about doing it properly. The prompt given to Claude covered the entire surface area at once: "Add Toss payment widget page /checkout/toss , success/fail redirect pages, /api/checkout/toss/confirm for server-side verification, update usePaywall