Software for Fintech
A fintech start-up is a software company that happens to move other people's money. The product can look finished in a demo and still be unsafe, because the hard part is invisible: what happens when a webhook arrives twice, a transfer times out halfway, or the balance on screen disagrees with the processor.
We supply engineers who build that invisible part. Payment flows, ledgers, reconciliation and the integrations with the providers you have chosen for identity checks, cards and bank transfers. Licences, regulatory permissions and audits are yours to obtain. We write code to the requirements that come out of them.
Bugs that cost a payments product real money
Each of these passes a demo. Each shows up in production, usually during a busy week.
The double charge
A customer taps Pay, the network stalls, the app retries. Without an idempotency key on the request, the processor sees two payments.
The balance stored as a number
A single balance column is updated in place. When two requests race, one update is lost and no record says which.
The webhook taken on trust
An endpoint that accepts any payload marked as paid, without verifying the signature or checking the event against the provider.
The half-finished transfer
Money leaves one wallet and the credit to the other fails. With no state machine, support staff repair it by hand in the database.
Reconciliation as an afterthought
Nobody compares the internal ledger with the settlement file until the accountant asks why they differ.
Components of a fintech back end
A double-entry ledger
Immutable entries that always sum to zero, with balances derived from them. Corrections are new entries, never edits.
Payment orchestration
Explicit states for each payment, safe retries, timeouts, refunds and chargebacks, with every transition logged.
Onboarding with identity checks
Screens and server logic that pass the applicant to your chosen KYC provider, store the outcome and route unclear cases to manual review.
Card and bank connections
Integration with a card issuer, an acquirer or an open-banking aggregator through their published APIs and sandboxes.
Daily reconciliation
Jobs that compare ledger, processor and bank files and raise each mismatch as a ticket with the evidence attached.
An operations console
Where your support and finance staff search a customer, see a payment's history and issue a refund under role limits.
Tools commonly used for this work
If your product already runs on something else, we work in that.
- Services
- Node.jsPythonPHP / LaravelGo
- Storage
- PostgreSQLRedis
- Messaging
- QueuesSigned webhooksScheduled jobs
- Apps
- ReactFlutterReact Native
- Delivery
- DockerGitHub ActionsAWS
Decisions that sit with the founders
We cannot make these for you and do not hold any licence you could rely on. Your legal adviser specifies, we build, your auditor assesses.
Your own licence or a partner's
Whether to apply for a payments or e-money authorisation, or to operate under a licensed sponsor bank or provider. It shapes the architecture.
How much card data you touch
Hosted fields and tokenisation from the processor keep most of PCI DSS outside your systems. Handling raw card numbers brings it all in.
Who performs KYC and AML checks
A third-party provider runs the document and sanctions checks, but the legal duty usually remains with the regulated entity.
Customer authentication
Strong Customer Authentication under PSD2 in Europe, additional-factor rules from the Reserve Bank of India, and equivalents in other markets.
Where records are kept
Some regulators insist that payment data stays inside the country. Pick the hosting region after that answer, not before.
What investors and partners will ask for
A sponsor bank or enterprise customer may expect a SOC 2 report or ISO 27001. Plan the evidence early, since it is gathered over months.
Should a start-up hire us for this?
It fits when
- You have a technical lead who sets direction and reviews pull requests.
- Providers are chosen, or you want help comparing their APIs.
- Runway makes a standing in-house team of specialists hard to justify yet.
- You accept that correctness work is slower than feature work.
It does not fit when
- You want a supplier to carry regulatory responsibility.
- The plan depends on launching before the licence question is settled.
- You need a trading engine with microsecond latency.
- No one on your side can describe how the money should flow.
Common queries from founders
Do you recommend a particular payment or KYC provider?
We will compare the documentation, sandbox quality and fee structure of the ones you shortlist. The commercial contract is between you and them.
Who holds the API keys?
You do. Provider accounts are opened by your company. Live keys sit in your secrets manager, and our engineers work against sandbox credentials unless you decide otherwise.
Can one engineer join our existing team?
Yes. We propose a named person, you interview them, and a small first task shows how they work before any longer arrangement.
What are the hourly rates?
Back-end work is $32 an hour and full-stack or mobile work $35. A full-time month is 160 hours, and the smallest retainer is 40 hours a month.
Do you work with blockchain or crypto assets?
That is quoted separately per engagement, and the regulatory position in your market needs to be clear first.
Draw the money flow and send it over
A sketch of who pays whom, through which provider, is enough to start a useful conversation. Our answer reaches you inside one business day.