If you're a solo dev outside the US, "just add Stripe" is rarely just. Stripe doesn't onboard sellers directly in a lot of countries, so you reach for a Merchant of Record (MoR) like Polar or Lemon Squeezy — and then you hit the second wall: the official SDK throws fetch failed the moment you deploy to a serverless platform like Vercel. I shipped paid checkout on two live products this way and got tired of re-solving the same problems. Here's the pattern that actually works in production....