Senior Backend Developer (UK) — Fintech, Wallet, Safeguarding, Payments & FX Experience

About Juuli Juuli is an AI-native fintech platform built exclusively for UK&Europe’s 43M+ solopreneurs. We bring payments, cards, FX, invoicing and tax automation into one place, with 90-second onboarding and AI at the core of the product. We are a lean, London-based team, and every senior hire here has a direct impact on how we grow. The Role You will own the technical core of Juuli’s e-money operations: wallets, ledger, safeguarding, payments and FX, built on PHP and MySQL. You will be part of our governance structure, making sure the systems that hold and move customer money are correct, auditable and ready for regulatory scrutiny. You will work directly with the founders and our compliance team. What You’ll Do Design, build and run our e-money platform in PHP and MySQL: wallets, double-entry ledger, balances, holds and fund flowsModel financial data in MySQL with strict correctness: transactions, locking, isolation levels and idempotent writesBuild safeguarding into the system: segregation of customer funds, daily reconciliation, break detection and reportingDesign and integrate payment flows across payment schemes (e.g. SEPA, Faster Payments), card programmes and our licensed partners’ APIsBuild FX capabilities: multi-currency balances, conversion, pricing and settlementTake part in governance: provide technical input to risk, compliance, safeguarding, incident and audit processesDocument our systems and controls clearly for compliance, auditors, partners and regulatorsSet engineering standards for reliability, testing, auditability, security and observabilityWork closely with product, compliance and fraud teams to build controls into the product by designReview code, mentor engineers and shape how we buildOur stack: PHP, MySQL What We’re Looking For Based in the UK with the right to work in the UK6+ years in backend development, including 5+ years of professional PHP (modern PHP 8.x, object-oriented design, automated testing)Strong MySQL expertise: schema design, InnoDB transactions, locking and isolation levels, indexing, query tuning and safe migrations on large tablesSignificant professional experience in fintech, payments or e-moneyProven experience building wallet and ledger systems in production: double-entry accounting, balances, holds, reversalsHands-on experience with safeguarding or client-money reconciliation in a regulated firmStrong experience with payment flows and integrations: schemes, processors, card programmesPractical experience with FX and multi-currency systemsSolid fundamentals in data consistency, concurrency, idempotency, queues and event-driven designComfort explaining system design and controls to non-engineers, including compliance, auditors and regulatorsClear communication and excellent English