Engineering Blog

How we build banking infrastructure from scratch — Event Sourcing, ISO 20022, BIAN, and the engineering decisions behind every API.

I quit my job, burned my savings, and built a core banking from scratch. Here's what I learned.

Gustavo Armoa

CTO & Principal Software Architect

I walked away from a CTO seat, burned through my savings, and spent four years building a core banking system that the industry said was impossible. Event Sourcing, native ISO 20022, BIAN, Kafka — from the ground up. No wrappers. No shortcuts. This is what happened.

I quit my job, burned my savings, and built a core banking from scratch. Here's what I learned.

Payments

How split payments work for marketplaces — and why most implementations are wrong

Gustavo ArmoaCTO & Principal Software Architect

A deep dive into atomic split payments: how a single buyer payment becomes N seller credits, platform fee collection, and escrow management — all in one API call. Why naive implementations break under chargebacks, partial refunds, and multi-seller carts. The ledger architecture behind splits that actually work at scale.

Compliance

ISO 20022: the future of financial messaging in Brazil — and why translation layers are technical debt

Gustavo ArmoaCTO & Principal Software Architect

Why we chose to build ISO 20022 natively — not as a translation layer. 19 native message types, SWIFT migration readiness, pacs.008 for credit transfers, camt.053 for account statements, and what it means for Brazilian fintechs building cross-border payment infrastructure.

Engineering

Multi-PSTI architecture: how we guarantee 99.99% uptime on PIX — and what happens when a PSTI goes down

Gustavo ArmoaCTO & Principal Software Architect

Our PIX infrastructure connects to 3 PSTIs simultaneously with automatic failover in < 1s. Circuit breakers, store-and-forward queues, health scoring, and the engineering decisions behind a payment system that hasn't dropped a single PIX transaction in 18 months.

Product

Entering Brazil? Here's the regulatory minefield Stripe, PayPal, and Temenos don't warn you about.

Gustavo ArmoaCTO & Principal Software Architect

Brazil is the world's 5th largest payments market — and a black box for foreign players. CADOC reports, CCS registries, judicial account freezes, PLD/FT compliance, MED 2.0 chain blocking. Companies like Stripe, PayPal, and Temenos spend millions and years navigating it. We built a single API layer that handles all of it in < 5ms.

Engineering

Ledger double-entry: how we designed an accounting engine that never loses a centavo

Gustavo ArmoaCTO & Principal Software Architect

Every transaction in Revenu generates automatic double-entry postings. Here's how our 11-engine ledger handles multi-currency, COSIF compliance, real-time reconciliation, and why most fintech ledgers are ticking time bombs. The architecture behind a ledger that has processed R$ 8 billion with zero balance discrepancies.

Payments

How we increased recovery rate to 94% with smart dunning

Gustavo ArmoaCTO & Principal Software Architect

Multi-channel dunning with progressive escalation: email → SMS → WhatsApp → payment retry → protest. How configurable collection rules recovered R$ 2.3M in Q1. The architecture behind a dunning engine that understands payment behavior, optimizes retry timing, and turns delinquent receivables into recovered revenue.

Compliance

How Open Finance data transformed our credit scoring engine

Gustavo ArmoaCTO & Principal Software Architect

How we use Open Finance data to enrich credit scoring: bank statements, income verification, and spending patterns — all consented, all via API. Why bureau-only scoring rejects 30% of creditworthy applicants, and how real-time financial data changes underwriting forever.

Infrastructure

Cash forecasting with AI: how TreasuryOS reduced idle cash by 40%

Gustavo ArmoaCTO & Principal Software Architect

Our ML models predict cash flows 7, 30, and 90 days ahead with 94% accuracy. How we train on historical patterns, account for seasonality, automate multi-bank sweeps, and turned R$ 47M in idle cash into yield-generating positions — all via API.

Product

Financial testing in sandbox: how we achieved zero production incidents

Gustavo ArmoaCTO & Principal Software Architect

Our sandbox is a 1:1 replica of production — same APIs, same edge cases, same behavior. Time travel, chaos injection, deterministic webhooks, and the testing philosophy behind 18 months of zero payment-related production incidents.

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