FinTech Web Application Developer

Most fintech teams treat compliance as a documentation exercise that happens at the end. The teams that ship cheaply and quickly treat it as the first architectural constraint. Tokenize cards in the browser using Stripe Elements or equivalent so cardholder data never touches your servers — you move from a Level 1 PCI audit to a SAQ-A questionnaire and save roughly £40,000 in annual audit cost.

SOC 2 controls follow the same pattern. Build access management, encryption at rest, audit logging, and change management into the platform before you have a single customer. Retrofitting these controls after the fact typically costs 3–4× more and takes 6–9 months of engineering time you cannot spare.

Open Banking and PSD2 integrations should be wrapped behind your own abstraction layer from day one. We've migrated clients between TrueLayer, Tink, and Plaid multiple times — each migration took under three weeks because the original architecture treated providers as swappable, not load-bearing.

Most fintech bugs that reach customers are ledger drift, not UI defects. Double-entry bookkeeping at the application layer, immutable transaction logs, and idempotent webhook handlers are non-negotiable. Build a reconciliation job that runs hourly and pages on any discrepancy greater than a penny — and treat any page from that job as a P0 incident, not a backlog item.

Idempotency keys on every state-changing endpoint are the single highest-ROI engineering practice in fintech. A retried webhook from Stripe should never debit a customer twice. The cost of getting this wrong is not the duplicate charge — it's the trust collapse when a customer realises your platform isn't deterministic.

Identity verification (Persona, Onfido), transaction fraud scoring (Stripe Radar, Sift, Sardine), and sanctions screening (ComplyAdvantage, Refinitiv) should each sit behind their own interface. Vendor pricing in this category moves quarterly; the firms that survive scale-up economics are the ones that can switch providers without a re-architecture.

Risk thresholds should be configurable at runtime, not deploy-time. Your fraud team will need to tune them weekly during the first six months of operation, and a deployment pipeline is the wrong granularity for that work.