Senior Backend Engineer - Credit Card Payments

Senior Backend Engineer - Credit Card Payments Hybrid in London, United Kingdom We're looking for a Senior Backend Engineer to join the Payments Infrastructure team. You’ll design and build the payments platform behind iwoca’s business credit card – the services that approve each payment, monitor transactions for fraud, and pay out cashback. The company Small businesses move fast. Opportunities often don’t wait, and cash flow pressures can appear overnight. To keep going, and growing, SMEs need finance that’s as flexible and responsive as they are. That's why we built iwoca. Our smart technology, data science and five-star customer service ensures business owners can act with the speed, confidence and control they need, exactly when it's needed. We’ve already cleared the way for 100,000 businesses with more than £4 billion in funding. Our passionate team is driven to help even more SMEs succeed, through access to better finance and other services that make running a business easier. Our ultimate mission is to support one million SMEs in their defining moments, creating lasting impact for the communities and economies they drive. The team iwoca launched its business credit card in 2026. It gives small businesses a fast, flexible way to pay for what they need and control their cash flow, alongside iwoca’s loans. The card is a core part of iwoca’s long-term growth. The Payments infrastructure team builds iwoca’s card payments platform. Its job is to approve each payment in moments when a customer uses their card. The team also builds the platforms that pay out rewards as customers spend and monitor every transaction. The team is small – a principal engineer, a product manager with a background in payments, and you. It works closely with iwoca’s ledger, fraud and customer product teams. The role As a senior backend engineer, you’ll own services and projects end to end, and shape the platform’s architecture with the principal engineer, from service boundaries to how authorisation, rewards, and transaction monitoring fit together. You’ll work closely with product to decide what the team builds and how. There’s still plenty to build, and you’ll take new services into production. You’ll build on your payments expertise alongside the principal engineer, with scope to grow as the platform matures. Most of the challenge is technical: scaling payments within card scheme rules and the regulation iwoca has to meet. Your code will run every time a small business uses its iwoca card. Live project examples: • Payment authorisation. Extending the service built to approve or decline each card payment in real time, using data held in other services. It places a hold on available credit in the ledger and applies iwoca's own checks, such as account status, merchant category code restrictions, and spend limits. • Transaction monitoring. Building the service that will screen card transactions for fraud and financial-crime risk as customers spend, so iwoca will rely less on third parties. • Rewards. Extending the service that pays out cashback, as the team adds to what the card offers. • Testing for failure. Designing sandbox tests that cover edge cases and failures across the card transaction lifecycle. • Ledger cutover and go-live. Moving the card platform onto iwoca's own ledger and infrastructure with as little downtime as possible, then fixing the issues that only show up in production. The requirements Essential: • Payment systems. You've designed and run highly available, low-latency payment systems in production, ideally on the issuing side. • Card payment flows. You've worked on card authorisation and clearing, and traced transactions from the terminal, through the acquirer and card scheme, to the issuer. You've used response codes to