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 diagnose declined transactions.

• Backend engineering. You have deep expertise in at least one object-oriented language. You've written and run backend services in it.

• Distributed systems. You've built microservices, REST APIs, and asynchronous messaging with queues or topics, and designed the database schemas behind them, ideally in PostgreSQL.

• AI leverage. You've built agentic workflows, or used AI to scale your engineering output beyond what you could deliver alone, at work or in your own projects. You judge when to use it and when not to, and you check its output before it reaches production.

• Communication. You write and speak clearly, directly, and concisely. You adapt technical detail to your audience.

Bonus:

• Ledgers and clearing. You've worked on a ledger, reconciliation, or clearing system – for cards, loyalty points, bank transfers, or money remittance.

• Testing. You've written automated tests for payment systems, ideally test-first.

• Python. You've used Python in production. It's the language the team works in.

The salary

We expect to pay from £100,000 to £120,000 for this role. But, we're open-minded, so definitely include your salary goals with your application. We routinely benchmark salaries against market rates, and run quarterly performance and salary reviews.

The culture

At iwoca, the best idea wins. We model our culture on independent thinking, challenging untested logic, and evidence-based decisions. We prioritise learning and growth, and give people the autonomy to develop in the direction that makes them most effective.

We're a tech company and believe in the power of AI to help us work faster and better. We provide the infrastructure where every iwocan always has access to the best models and where those models have access to all of our data. We will help our people to learn how to use and grow with the new tools available to them.

The offices

We put a lot of effort into making iwoca a great place to work:

• Offices in London, Leeds, Berlin, and Frankfurt with plenty of drinks and snacks.

• Events and community-led groups, including running groups, padel, and monthly ping-pong and pool competitions.

The benefits

• Flexible working hours.

• Medical insurance from Vitality, including discounted gym membership.

• A private GP service (separate from Vitality) for you, your partner, and your dependents.

• 25 days’ holiday per year, an extra day off for your birthday, the option to buy or sell an additional five days of annual leave, and unlimited unpaid leave.

• A one-month, fully paid sabbatical after four years.

• Instant access to external counselling and therapy sessions for team members that need emotional or mental health support.

• 3% Pension contributions on total earnings.

• An employee equity incentive scheme.

• Generous parental leave and a nursery tax benefit scheme to help you save money.

• Electric car scheme and cycle to work scheme.

• Two company retreats a year: we’ve been to France, Italy, Spain, and further afield.

And to make sure we all keep learning, we offer:

• A learning and development budget for everyone.

• Company-wide talks with internal and external speakers.

• Access to learning platforms like Treehouse.

Useful links:

• iwoca benefits & policies

• Interview welcome pack