Fintech Developer
Hire a fintech developer for payments and financial systems
The money layer, built with the paranoia it deserves. Signed webhooks, idempotent handlers, integer minor units, append-only ledgers, row-level locks. The boring rules that prevent the entire class of "the numbers do not add up" tickets.
The part most people get wrong
Every payment integration has a happy path that takes an afternoon and an edge-case surface that takes weeks — duplicate webhooks, partial refunds, chargebacks, currency conversion, installments, split payouts, tax compliance. Most freelancers ship the afternoon version. The difference surfaces in month one of real volume.
What you get
- →Stripe — Checkout, Billing, Connect for marketplace payouts, Split for automated commission distribution, MSI (meses sin intereses) for Mexican cards.
- →MercadoPago with HMAC signature verification, transaction-ID idempotency and replay protection. Skipping signature verification is the most common payment bug in LATAM.
- →Payway / Decidir as a second Argentine card rail alongside MercadoPago.
- →AFIP electronic invoicing (RG 5616) via WSFEv1 SOAP with your own X.509 certificate — zero rejections across Distrialma's production volume since 2026-03.
- →Reconciliation engines that cross-reference bank statements against internal records and surface only the discrepancies.
- →Financial PDF parsing across dozens of bank statement formats.
- →Internal wallet and escrow with an immutable append-only ledger — a balance is the sum of its entries, never a mutable column.
- →Money stored as integer minor units, never floats. Every money write takes a row-level lock.
Proof — shipped and in production
ArTicket Platform
A ticketing operator was renting its platform. The own 2D canvas seat-map engine runs at 39fps on 10k+ seats, and the operator owns it now.
Financial PDF Processor
Banking statement PDFs were parsed by hand across dozens of accounts. Streamlit MVP now extracts and cross-references transactions automatically.
BookProof
Authors buying Amazon reviews got flagged in bulk. Weekly automatic queue delivery, reader anonymity, 72h deadlines and 14-day replacement — no flags.
Distrialma Wholesale ERP
A wholesaler was running its POS blind to accounting. An ERP layered over the SQL Server POS shows a live balance sheet and files AFIP invoices.
Impact Processor CSR26
An ESG plastic-credit protocol needed dynamic weekly pricing and a 5/45/50 vesting rule on-chain. Stripe Split handles automated commission distribution.
Frequently asked
Which payment provider is right for LATAM?+
MercadoPago converts best in Argentina, Mexico, Brazil, Chile and Colombia because buyers already have accounts and it supports local installments. Stripe is better for marketplace payouts, sophisticated subscription logic and international cards. Serious projects usually run both.
What is the most common payment bug you fix?+
Unverified webhook signatures — anyone who finds the endpoint URL can forge a paid-order confirmation. Second is non-idempotent webhook handling: the provider retries on timeout and the handler double-credits the customer. Both are small fixes that nobody makes until it has already cost money.
How do you store money in the database?+
Integer minor units, never floating point. Ledger tables are append-only. Every money-touching write takes a row-level lock. Those three rules eliminate essentially every reconciliation bug before it exists.
This role is also called
- finance project expert
- payments engineer
- billing systems developer
- financial software developer
- banking integration developer
Start with a written brief
Describe what the business is losing today and what the target outcome looks like. I come back with a concrete plan against that document — in English, Spanish, Portuguese or Polish.
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