PaymentsFintechArchitecture

Cross-Border RateEngine

Technical Lead / CTO · Hizo Africa · 2023 — Present

The core pricing layer of Hizo's neobank — a cross-border rate engine driving FX conversion, internal rate sourcing, and liquidity routing across remittance and crypto flows.

LaravelPHPPostgreSQLRedisTypeScript

🔒 Source is private (production fintech). The architecture and decisions are documented below — happy to walk through detail in an interview.

The problem

Every money-movement product at Hizo — USDT-to-fiat remittance, crypto trading, card funding — needed a consistent, trustworthy price. Without a single source of truth for rates, each flow would invent its own FX math, drift apart, and expose the business to mispricing and loss. The RateEngine was built to be that single source of truth.

Constraints

Money-critical correctness — a wrong rate or a rounding bug is real financial loss. Decimal math had to be exact (this is the class of bug I caught in staging via assertion-level logging before it reached production).
Multiple inputs — rates sourced from PSPs and market feeds, blended into an internal rate with spread/margin rules.
Multiple consumers — remittance, crypto, and card flows all priced off the same engine, each with different tiering.
Freshness vs. stability — quotes had to be current but not flap on every tick; stale rates are a liability.

What I built

   Rate sources (PSPs, market feeds)
              │
              ▼
        ┌───────────────┐
        │  RateEngine   │  internal rate = source ± spread/margin
        │  (Laravel)    │  cached + versioned quotes (Redis)
        └───────┬───────┘
                │  one priced quote, audited
   ┌────────────┼─────────────┐
   ▼            ▼             ▼
 Remittance   Crypto       Card funding
 (USDT→fiat)  trading

A central rate-sourcing + blending layer producing an internal rate with configurable spread/margin.
Quote caching and versioning in Redis so consumers price off a stable, auditable snapshot rather than a live-moving number.
A single pricing contract consumed by remittance, crypto, and card funding — so a rate change propagates everywhere consistently.
Liquidity routing feeding payout decisions across local African rails.

The decision that mattered

Make the RateEngine the one place money is ever priced, and have every product depend on it rather than computing FX themselves. Centralizing pricing meant correctness, spread policy, and auditability lived in a single, testable system — instead of being re-implemented (and re-bugged) in every flow.

Impact

Powered pricing across remittance, crypto, and card funding from a single source of truth.
Caught a silent float-conversion bug in cross-border decimal math during staging, preventing a class of money-movement errors from reaching production.

Source code is private (production fintech). Architecture and decisions summarized here — happy to walk through detail in an interview.