Job Title: Software Engineer Department: Engineering & Product Development (EPD) Reports to: Engineering Lead Location: Singapore (Hybrid work arrangement) About Codex Codex is building the infrastructure for stablecoin-based cross-border payments — moving money faster, cheaper, and more transparently than the legacy financial system. Backed by Circle, Coinbase, Dragonfly, Wintermute, and Cumberland, we're a small team solving hard problems at the intersection of crypto and global payments. The Role You'll own the full lifecycle of how money moves through Codex — from the moment a customer onboards, through KYC/KYB and compliance checks, all the way to payment execution and settlement. You'll work directly with the founders and with our Trading Ops and Compliance teams to build systems that are fast, reliable, and compliant across every market we operate in. You'll have real influence over architecture, real ownership of a critical domain, and you'll be building things that matter from day one. Responsibilities 3P & Payment Integrations - Own the technical integration of third-party payment providers, including offramp/payout flows, API integration, and sandbox/testnet testing - Design and implement the architecture for how 1P and 3P flows interact, with careful consideration of coupling, maintainability, and risk - Integrate payment rails across the globe — banks, PSPs, and liquidity providers - Build the document storage and invoice pipeline to support 3P operational workflows - Coordinate with Legal and Compliance on open questions arising from 3P integration (e.g. balance holding, regulatory implications) Settlement, Reconciliation & Stablecoin - Build and maintain settlement, reconciliation, and ledger systems across fiat and crypto flows - Build stablecoin on/off-ramp flows and the crypto-specific compliance tooling that supports them Backend Architecture - Lead significant backend refactors to improve system correctness and maintainability - Design and maintain order management systems: cancellation logic, state validation, and payout flows for orders with pending manual payouts - Build internal ops tooling to surface pending manual payout queues to non-engineering teams, reducing trader workload Onboarding & Compliance Infrastructure - Build and maintain end-to-end onboarding infrastructure — KYC/KYB flows, identity verification integrations, and risk scoring - Own the KYT integration layer across fiat and crypto deposit and order workflows, in coordination with the Compliance team - Build transaction monitoring, AML, and sanctions screening systems - Maintain compliance data infrastructure — audit logs, reporting pipelines, and regulatory submissions - Implement KYT layering across 3P flows and contribute to design decisions on when and how it applies What we're looking for - 3 to 5 years of backend engineering experience, with meaningful depth in at least one of: payments/rails or compliance/onboarding - Strong system design instincts; you've built systems that handle failure gracefully and scale without becoming a maintenance burden - Experience working cross-functionally with compliance, legal, or operations teams - Comfortable with ambiguity — you can take a regulatory requirement or a business need and turn it into a well-designed technical spec - Someone who takes full ownership and moves fast without cutting corners Nice to have - Familiarity with both payment rails and compliance frameworks - Experience in crypto or stablecoin infrastructure — on-chain settlement, blockchain analytics tooling - Prior startup or scale-up experience where broad scope was the norm, not the exception