Project 08 · Backend for a fintech startup
The API behind a London payments startup's apps: a double-entry ledger, KYC onboarding, card and bank webhooks and an ops console, built and run by us.
- Market
- United Kingdom
- Year
- 2026
- Timeline
- 18 weeks
- Team
- 5 people · tech lead, 3 engineers, DevOps
- Delivered
- B2B · API · Admin console · On-call
- POST/ledger/transfers20142ms
- GET/accounts/{id}/balance20018ms
- POST/kyc/sessions20265ms
- POST/webhooks/cards20012ms
- GET/payouts?status=pending20027ms
- PATCH/customers/{id}20031ms
{
"id": "trf_8Hq2",
"amount": 2500,
"currency": "GBP",
"status": "settled"
}01
The challenge
A payments startup needs a back end that never loses track of money. It also has to onboard customers safely and react to card and bank events as they happen. The founding team wanted to focus on product, not infrastructure.
02
Our approach
We built a TypeScript API on PostgreSQL with a double-entry ledger at its core, documented end to end in OpenAPI. It runs on AWS, and we stay on call for it.
- 01
Double-entry ledger
Every movement of money is recorded as balanced entries, so balances can always be traced and reconciled.
- 02
KYC onboarding
Identity checks run through the API, with clear states the apps can show to users.
- 03
Card and bank webhooks
Card and Open Banking events are received, verified and applied to the ledger safely and in order.
- 04
Ops console
Support and finance staff can look up customers, review transactions and handle exceptions in one place.
Platforms
- REST API
- Ops console
- AWS
Technology
- TypeScript
- PostgreSQL
- Open Banking
- AWS
- OpenAPI