Senior Software Engineer, Back-end (Fraud)

Affirm is reinventing credit to make it more honest and friendly, giving consumers the flexibility to buy now and pay later without any hidden fees or compounding interest. The Fraud Engineering organization builds the foundational and tactical software that enables Affirm to respond strategically to fraud - both in real time and after the transaction. Our mission is to support business growth while protecting Affirm, our buyers, and our merchants.

We’re looking for a Senior Software Engineer to join our fully remote team based in Europe. You’ll collaborate closely with stakeholders across North America - including teams in Product, Compliance, Machine Learning, Fraud Operations, Fraud Strategy, and other Fraud Engineering teams. The Fraud International Team (FIT) leads the engineering effort to extend Affirm's Fraud Decisioning System into markets beyond the US - Canada, the UK, Australia, and growing rapidly. We own real-time fraud decisioning for these markets, integrate region-specific risk vendors, and are building the platform that lets Affirm stand up fraud protection in a new country quickly and safely.

• Own and deliver quarterly goals for your team, leading engineers through ambiguity to solve open-ended problems, and ensuring that everyone is supported throughout delivery.
• Design and implement real-time fraud decisioning services and APIs in Python or Kotlin, extending Affirm's Fraud Decisioning System to markets beyond the US.
• Build and evolve the platform and tooling that let Affirm launch fraud decisioning in a new country quickly—turning market-by-market setup (rules, models, and vendor configuration) into a repeatable, low-friction path so launches scale sub-linearly with the number of markets.
• Integrate region-specific fraud and risk vendors and help operationalize the machine learning and AI signals that power real-time decisioning, while using modern AI tooling to move faster as an engineer.
• Support peers and stakeholders across the product development lifecycle - collaborating with Product, Machine Learning, Analytics, and Fraud Strategy, articulating technical constraints, and partnering on decisions that properly weigh risks and trade-offs.
• Support the operations and availability of your team's systems by creating and monitoring metrics, escalating when needed, and contributing to keep-the-lights-on and on-call efforts.
• Foster a culture of quality and ownership - setting and improving code review and design standards, mentoring teammates, and leading by example.
• Participate in an on-call rotation as a requirement.

• 5+ years of experience building backend systems at scale using Python or Kotlin.
• Experience with distributed systems and infrastructure using AWS, MySQL/PostgreSQL, and Kubernetes.
• Strong system design skills and a track record of delivering maintainable, extensible services.
• Fluency with AI-driven engineering - every Affirm engineer builds with tools like Claude Code and most PRs are co-authored with AI, so directing and orchestrating AI and excelling in the reviewer's seat (setting intent, critically evaluating generated code, and owning its correctness, quality, and security) is a core expectation.
• Proficiency in SQL and working with data-rich environments.
• Familiarity with CI/CD practices and safe production deployments.
• Strong written and verbal communication skills, especially in distributed teams.
• A proactive, ownership-driven mindset with a focus on learning and team success.
• Experience with Snowflake, dbt, Airflow, or Chronosphere (nice to have).
• Background in fraud prevention, risk systems, or real-time decisioning (nice to have).
• Experience building for multiple markets or regions - internationalization or localization (nice to have).
• Experience working in the fintech sector or other highly regulated environments, with a strong understanding of risk, compliance, and operational constraints (nice to have).

Base Pay Grade - N, Equity Grade - 4. ESP base pay range per year: €86,000 - €122,000. Additional benefits include: Flexible Spending Wallets for tech, food and lifestyle, Away Days - wellness days to take off work and recharge, Learning & Development programs, Parental benefits, Employee Resource & Community Groups. Affirm covers all premiums for health care coverage for you and your dependents, offers competitive vacation and holiday schedules, and an ESPP (employee stock purchase plan) enabling you to buy shares of Affirm at a discount.

Remote Spain. Visa sponsorship is available for this role, but you must be based in Spain.