Custom Software Development for Fintech

Custom platforms for neobanks, lenders, wealth managers and payment companies: PSD2, MiCA, double-entry ledgers and idempotent APIs that survive an audit.

What Fintech Software Delivers

• A double-entry ledger that actually balances: Fintech buyers are usually founders who have raised seed-to-Series-B and need to either ship the first regulated product or rebuild the prototype that survived the licence application. The licence is granted, the BaaS partner (Solaris, Treezor, Modulr, Currencycloud) is signed, and now they realise the JavaScript ledger that worked for the demo is going to lose money. We come in to build the boring infrastructure that makes a fintech actually fintech: a real double-entry ledger, idempotent APIs, KYC and AML pipelines that pass the regulator, and operations tools that the support team can actually use without phoning engineering.
• PSD2 and Open Banking from day one: Strong Customer Authentication, dynamic linking, OAuth flows against TPP gateways, eIDAS QWAC and QSeal certificate handling. We have integrated with Berlin Group, STET and UK Open Banking specs, and against Spanish AISP/PISP gateways like Redsys and Cecabank.
• KYC and AML pipelines that pass the regulator: Onfido, Veriff or Jumio for ID verification, ComplyAdvantage / Refinitiv for sanctions and PEP screening, transaction monitoring rules tuned per risk segment, SAR generation in the format your FIU actually accepts (SEPBLAC in Spain, FinCEN in the US).
• BaaS and card programmes wired correctly: We have launched on Solaris, Treezor, Modulr, Railsr and Swan, with card programmes on Marqeta, Stripe Issuing and Galileo. The integration is the boring part. The value is in webhook idempotency, retry logic and the reconciliation tooling we ship around it.
• Crypto-fiat rails when MiCA actually allows it: For MiCA-licensed CASPs we build custody integrations (Fireblocks, BitGo, Copper), on/off ramps with Stripe Crypto or BCB, travel rule compliance via Notabene or Sumsub, and the Title VI reporting that ESMA expects. We will tell you when MiCA does not allow what you want. That conversation has saved clients money.
• Operations tooling support actually uses: Customer support consoles with full case context, freeze/unfreeze/limit-override flows with four-eyes approval, refund and chargeback workflows, and a back-office that lets ops act in seconds. We have seen too many fintechs where every ops action is a Slack message to engineering.

How We Build Your Fintech Software

1. Regulatory perimeter mapping: Before architecture we list every regulator your product touches (Bank of Spain, CNMV, ESMA, FCA, BaFin, OCC) and what each one expects in terms of capital, reporting and operational resilience.
2. Ledger and money-flow design: We diagram every account, every leg of every transaction, and every reconciliation point against your BaaS and acquirer. This document becomes the source of truth that audit, finance and engineering all read.
3. Idempotency and reliability spine: Every payment endpoint takes an idempotency key. Every external call retries with exponential backoff and a circuit breaker. Every webhook is verified, deduplicated and stored. This is what makes the difference between losing money once and never losing it.
4. Compliance build-out: KYC onboarding, ongoing AML monitoring, transaction risk scoring, suspicious activity reporting, audit log immutability, all built as a separate module so it can be audited end-to-end.
5. External penetration test and chaos drill: Pre-launch penetration test against OWASP API Top 10 and PCI-DSS where applicable, plus a chaos engineering drill where we kill the BaaS connection mid-payment to make sure the system recovers cleanly.
6. Go-live with a real-money pilot: We open the system to a small set of internal users moving real money in the low hundreds of euros. One week of clean reconciliation later, we open the gate.

High-performance stack used by global leaders

React/Next.js/Angular on the frontend and Java 21 + Spring Boot + PostgreSQL 14 on the backend: the same stack that BBVA, ING, and Netflix use for their security and performance.

Fintech Software: FAQ

How much does it cost to build a fintech software product?

A focused MVP (onboarding + KYC + a wallet on top of a BaaS) typically lands between €60,000 and €120,000. A neobank-style product with cards, payments and an ops console runs €180,000-€400,000. A regulated lending platform with credit decisioning and servicing usually starts around €250,000. The wide range comes from the licence model: BaaS-fronted is cheap, your own EMI/PI licence is expensive.

How long does implementation take?

First production transaction in 16-24 weeks for a BaaS-fronted product. Full feature parity with what you pitched in the deck typically takes 9-14 months. Anything faster is usually skipping the controls a regulator will ask about later.

Are you familiar with PSD2, MiCA and AML directives?

Yes. PSD2 plus EBA RTS on SCA and CSC, the EMD2 framework for EMIs, MiCA Title II/III/IV/V/VI for crypto-asset services, and the AML5/AML6 directives plus the upcoming AMLR/AMLD6 package. For Spanish projects we work hand in hand with the legal team on Banco de España and SEPBLAC requirements.

Can you integrate with our BaaS or core banking provider?

Yes. We have shipped integrations with Solaris, Treezor, Modulr, Currencycloud, Railsr, Swan, ClearBank and Mambu. For card programmes, Marqeta, Stripe Issuing and Galileo. For payments, Stripe, Adyen, Redsys, GoCardless and Trustly. If your provider has any documented API, we connect to it.

How do you handle data residency and customer privacy?

EU customer data stays in EU regions. KYC documents are encrypted with envelope encryption and a customer-managed KMS key, with strict access logs reviewed monthly. We segregate prod and non-prod completely and never use real customer data in lower environments: synthetic data only.

How do you handle PCI-DSS scope?

We design to minimise PCI scope. PAN never touches your servers. We use hosted iframes (Stripe Elements, Adyen Components) or tokenisation at the BaaS layer. When we have to enter scope (full PAN handling for issuing) we run a dedicated cardholder data environment with the network segmentation a QSA expects to see.

Can you build the credit decisioning engine?

Yes. We have built rule engines combining bureau data (Experian, Equifax, ASNEF in Spain), open banking transaction analysis, and ML scoring models. Decisions are explainable: every accept/reject ships with the rules that fired and the bureau evidence, which you will need under the EU AI Act when it kicks in.

What happens if your engineer pushes a bug that loses money?

It should not happen because of how we build: every money-moving change is gated by automated property-based tests on the ledger, plus mandatory four-eyes review. If it ever did, our process is simple: stop the bleed, replay the journal to recover state, write the post-mortem, fix the test gap. We carry professional liability insurance and our contracts make our responsibility explicit.

Do you work with clients globally?

Yes. We work fully remote with clients across Spain, Europe, the US and LATAM. Time zones, video calls and live demos at every milestone.