Senior Backend Engineer - Credit Card Payments

Description

The company provides finance to small businesses, having helped over 100,000 of them with more than £4 billion in funding. It launched a business credit card in 2026 alongside its loans, and the card is central to its long-term growth.

You will join the Payments Infrastructure team as a senior backend engineer to design and build the card platform: the services that approve each payment, monitor transactions for fraud and pay out cashback.

The team is small, made up of a principal engineer, a product manager with a payments background, and you. It works alongside the ledger, fraud and customer product teams.

The company is a tech business that gives everyone access to the best AI models, with those models able to reach all of its data, and it helps staff learn to use new tools. Ideas are judged on evidence and are open to challenge, and people are given the freedom to grow in the direction that suits them best.

Responsibilities

• Own services and projects from start to finish, and help the principal engineer shape the architecture, including service boundaries and how authorisation, rewards and transaction monitoring connect.
• Work with product to decide what the team builds and how it builds it.
• Take new services into production.
• Scale payments within card scheme rules and the regulation the company must meet.
• Extend the real-time service that approves or declines each card payment, using data from other services. It places holds on credit in the ledger and applies the company's own checks, such as account status, merchant category code restrictions and spend limits.
• Build a service that screens card transactions for fraud and financial-crime risk as customers spend, reducing reliance on third parties.
• Extend the cashback service as the team adds features to the card.
• Design sandbox tests that cover edge cases and failures across the card transaction lifecycle.
• Move the card platform onto the company's own ledger and infrastructure with minimal downtime, then fix the problems that only appear in production.
• Your code runs each time a small business uses its card, and there is room to grow as the platform matures.

Requirements

• Essential: you have designed and run highly available, low-latency payment systems in production, ideally on the issuing side.
• Essential: you have worked on card authorisation and clearing, traced transactions from terminal through acquirer and card scheme to issuer, and used response codes to diagnose declines.
• Essential: you have deep expertise in at least one object-oriented language and have written and run backend services in it.
• Essential: you have built microservices, REST APIs and asynchronous messaging with queues or topics, and designed their database schemas, ideally in PostgreSQL.
• Essential: you have used AI to build agentic workflows or to scale your output beyond what you could do alone, at work or in personal projects. You know when to use it, and you check its output before it reaches production.
• Essential: you write and speak clearly, directly and concisely, and you adapt technical detail to your audience.
• Bonus: you have worked on a ledger, reconciliation or clearing system for cards, loyalty points, bank transfers or money remittance.
• Bonus: you have written automated tests for payment systems, ideally test-first.
• Bonus: you have used Python in production, the language the team works in.

Conditions

Salary of £100,000 to £120,000. Salaries are benchmarked against market rates, and performance and pay are reviewed quarterly.

Hybrid working in London, United Kingdom, with offices also in Leeds, Berlin and Frankfurt.

Flexible working hours.

Benefits

• Medical insurance through Vitality, including discounted gym membership.
• A private GP service, separate from Vitality, for you, your partner and your dependents.
• 25 days of holiday a year, an extra day off on your birthday, the option to buy or sell 5 days of annual leave, and unlimited unpaid leave.
• A one-month fully paid sabbatical after four years.
• Immediate access to external counselling and therapy for emotional or mental health support.
• Pension contributions of 3% of total earnings.
• An employee equity incentive scheme.
• Generous parental leave and a nursery tax benefit scheme.
• Electric car scheme and cycle to work scheme.
• Two company retreats a year.
• A learning and development budget for everyone, company-wide talks from internal and external speakers, and access to learning platforms such as Treehouse.
• Drinks and snacks in the offices, plus events and community groups, including running, padel, and monthly ping-pong and pool competitions.