Payment Gateway (Stripe-like) — Simple

Problem statement (interviewer prompt)

Design a Stripe-style payment gateway: merchants integrate a checkout SDK, you authorise + capture cards, route to the right acquirer/network, run real-time fraud scoring, expose webhooks for events, and maintain a double-entry ledger that reconciles daily.

flowchart LR
  M[Merchant]
  GW[Payment API]
  TOK[Tokenization]
  AUTH[Authorization]
  PSP[Acquirer / Network]
  ISS[Issuer Bank]
  REC([Reconciliation])
  M --> GW --> AUTH --> PSP --> ISS
  GW --> TOK
  GW --> REC

    classDef client fill:#dbeafe,stroke:#1e40af,stroke-width:1px,color:#0f172a;
    classDef edge fill:#cffafe,stroke:#0e7490,stroke-width:1px,color:#0f172a;
    classDef service fill:#fef3c7,stroke:#92400e,stroke-width:1px,color:#0f172a;
    classDef datastore fill:#fee2e2,stroke:#991b1b,stroke-width:1px,color:#0f172a;
    classDef cache fill:#fed7aa,stroke:#9a3412,stroke-width:1px,color:#0f172a;
    classDef queue fill:#ede9fe,stroke:#5b21b6,stroke-width:1px,color:#0f172a;
    classDef compute fill:#d1fae5,stroke:#065f46,stroke-width:1px,color:#0f172a;
    classDef storage fill:#e5e7eb,stroke:#374151,stroke-width:1px,color:#0f172a;
    classDef external fill:#fce7f3,stroke:#9d174d,stroke-width:1px,color:#0f172a;
    classDef obs fill:#f3e8ff,stroke:#6b21a8,stroke-width:1px,color:#0f172a;
    class M,GW,TOK,AUTH,PSP,ISS service;
    class REC compute;