Clarifying questions first: What does the existing payments backend already support? Are any of the five methods already integrated, or would all five be net-new? What exactly counts as "launch" in 3 weeks — all five methods at 100%, a limited rollout, or a feature-flagged release? Which countries, currencies, and devices must be supported at launch, since each payment method has different requirements? Are merchant accounts, contracts, and credentials already in place for all five providers? Can scope be reduced if all five methods cannot be delivered safely in 3 weeks? There is a clear tension between the fixed date, the five-method requirement, and a two-engineer team with no dedicated QA. Phased milestone breakdown: Phase 1: Feasibility and scope lock, inventory backend capability for each method, verify provider readiness, define fallback scope. Phase 2: Payment architecture, define a normalized payment-method model. Phase 3: Checkout UX design, smallest coherent flow, not a full redesign. Phase 4: Backend/provider integration, broken out per provider. Klarna and bank transfer flagged as needing product definition before engineering starts. Phase 5: Frontend implementation. Phase 6: Testing, explicitly owned by the 3-person team since there's no dedicated QA. Phase 7: Controlled launch with per-method kill switches if the architecture allows it. Risks and open questions: Project-threatening: Five integrations may not fit the fixed launch date. This should be treated as a business decision, not hidden as an engineering execution problem. Project-threatening: External provider approval could miss the launch regardless of engineering progress. Project-threatening: Bank transfer is currently undefined and cannot be responsibly scoped until clarified. Manageable: Provider-specific UX differences and partial provider outages. What's NOT included: This plan does not assume a redesign of cart, shipping, or promotions, does not assume a dedicated QA hire, and does not treat five methods in three weeks as automatically feasible.