Service · Fintech

Fintech Development

Event-sourced ledgers. Escrow state machines. Built for regulators and auditors.

Financial software has zero tolerance for 'mostly correct'. I build fintech backends the way auditors want to read them: for a US fintech startup's SEC Regulation CF crowdfunding platform, that meant an event-sourced ledger with 31 event types, a 6-state escrow machine, 28 database models, 30 documented endpoints, and 248 passing tests — with zero production bugs.

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The challenge

A race condition in payment processing isn't an embarrassing bug — it's a regulatory event. Every financial system I ship is built on serializable transactions, idempotent operations, and append-only audit trails. A fintech client on a current engagement described the work as “Financial-grade integrity… serializable transactions, idempotency, and audit-safe design patterns.” That's the bar, on every project.

What I build

Event-Sourced Ledgers

Append-only, double-entry ledger design where every balance is reconstructable from its history

Escrow & Payment Flows

Explicit state machines for held funds, releases, refunds, and every failure path

Regulated Platform Backends

Crowdfunding (SEC Reg CF), investment, and marketplace platforms with compliance designed in

Payment Integrations

Stripe and payment-provider integrations with idempotent, replay-safe webhook handling

KYC & Onboarding Flows

Identity verification, role-based access, and consent flows for regulated products

AI-Assisted Fintech Products

Deal matching, document OCR, and datarooms — as built for the Continuity M&A marketplace

Web3 & Blockchain Integrations

Wallet connections (MetaMask, WalletConnect), ERC-20/721 token display, DeFi protocol interfaces, and on-chain data indexing — frontend and API layers, alongside your smart-contract auditor

Tech stack

TypeScriptNode.jsPostgreSQLReactSupabaseStripeClaude APIRedisDocker

Which of my builds proves this

CLO Dashboard Copilot

Azure OpenAI copilot over approved compliance data — grounded answers, guardrails, and per-request cost control (ongoing).

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Fintech Escrow & Event-Sourced Ledger Backend

Two fintech backends — a Regulation CF platform for a US fintech startup (31 event types, 28 database models, 30 documented endpoints, 248 passing tests, zero production bugs) and a tokenized investment platform (54 event types, securities tokenization, 15-role access control, 1,820 test cases, ongoing). Both on a 6-state escrow machine.

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Continuity — Belgian M&A Marketplace

React/Supabase platform with a Claude-powered matching engine, OCR dataroom, digital NDA flow, 4 registry API integrations, 5 roles, 6 tiers, and 3 languages — first of its kind in the Belgian SME market. Live at continuity.deals.

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Related services

Integrations

Stripe, escrow, ledgers, and webhooks built to be idempotent and auditable.

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Fractional CTO

Architecture and technical due diligence for regulated financial products.

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Maintenance & Retainers

Ongoing support and monitoring once money is moving through the system.

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How we work

Most MVPs ship in 3–6 weeks; complex platforms are scoped individually once the requirements are clear.

01

Intro Call

A 30-minute conversation about your project, goals, and timeline. No commitment either way.

02

Scoped Proposal

A written scope, architecture outline, and quote. I respond to every message within 24 hours.

03

Weekly Demos

You see working software every week, with written progress updates in between. No black boxes.

04

Ship & Handover

Deployment, documentation, and a clean handover — you own everything I build.

Compliance & standards

SEC Reg CF (platform experience)PCI-DSS scope minimisationAML/KYC patternsGDPRAppend-only audit trails

Frequently asked questions

How do you make sure money never goes missing?
By never storing a balance as a mutable number. An event-sourced, double-entry ledger records every movement as an immutable event — the Reg CF platform's ledger uses 31 distinct event types — so every cent of every balance is reconstructable and auditable. Combined with serializable transactions and idempotent operations, the failure modes that lose money simply have nowhere to hide.
What is an event-sourced ledger, and why does it matter?
Instead of updating an account row in place, you append events — deposit received, funds held, investment committed, refund issued — and derive balances from the event stream. It matters because regulators and auditors don't want your current numbers; they want proof of how you got them. Event sourcing makes that proof a query, not a forensic investigation.
How do you handle escrow?
Escrow is a state machine, not a boolean. The crowdfunding backend models it in 6 explicit states with legal transitions between them, idempotent handlers on every transition, and an audit event for every movement of funds. Illegal transitions are rejected at the type and database level, so held funds can't be released twice or refunded from the wrong state.
Can you work on SEC-regulated platforms?
Yes — I built the backend for a US SEC Regulation CF crowdfunding platform: 30 documented endpoints, 28 database models, 248 passing tests, and zero production bugs. I work alongside your counsel: legal defines the rules, and I make the system provably enforce them.
How do you test financial systems?
The Reg CF backend ships with 248 passing tests: money-math tests around rounding and allocation, integration tests against a real database, idempotency tests that replay every webhook twice, and failure-path tests for every escrow transition. Financial code earns trust through its test suite — a client review of a current engagement specifically called out the serializable transactions, idempotency, and audit-safe design patterns.
Do you work on Web3, crypto, and DeFi projects?
Yes. I build the application layer for Web3 products: wallet integrations (MetaMask, WalletConnect), ERC-20 and ERC-721 token display, DeFi protocol interfaces (Uniswap, Aave), and on-chain data indexing with The Graph. I focus on the frontend and API layers that make a protocol usable — and I work alongside a specialist auditor for the smart contracts themselves, rather than writing unaudited contract code.
How long does a fintech build take?
MVPs typically take 3–6 weeks; larger, complex platforms are scoped individually once the requirements and compliance surface are clear. You'll get a realistic timeline with your written proposal.
What does a fintech build cost?
Most engagements start around $5K; smaller well-scoped work is considered case-by-case. Book a call or email me and you'll have a reply within 24 hours.

Ready to start?

Book a free 30-minute call. No sales pitch — just a direct conversation about your project.

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Or email: contact@waseemahmad.dev