Senior Software Engineer, Back-end (Fraud)

Affirm is a company reinventing credit to make it honest and friendly by offering buy now, pay later without hidden fees or compounding interest. The Fraud Engineering organization builds software to strategically respond to fraud in real time and post-transaction, supporting business growth while protecting the company, customers, and merchants. The Fraud International Team extends Affirm's Fraud Decisioning System beyond the US to Canada, the UK, Australia, and other markets, focusing on real-time fraud decisioning and integration of region-specific risk vendors.

• 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 with a track record of maintainable, extensible services.
• Fluency with AI-driven engineering and experience critically evaluating AI-generated code.
• Proficiency in SQL and data-rich environments.
• Familiarity with CI/CD practices and safe production deployments.
• Strong written and verbal communication skills in distributed teams.
• Proactive, ownership-driven mindset focused on learning and team success.

Nice to have:

• Experience with Snowflake, dbt, Airflow, or Chronosphere.
• Background in fraud prevention, risk systems, or real-time decisioning.
• Experience building for multiple markets with internationalization or localization.
• Experience in fintech or other regulated environments with risk, compliance, and operational constraints understanding.

• Own and deliver quarterly goals, leading engineers through ambiguous, open-ended problems.
• Design and implement real-time fraud decisioning services and APIs in Python or Kotlin.
• Build and evolve platform and tooling to enable scalable fraud decisioning launches in new countries.
• Integrate region-specific fraud and risk vendors and operationalize machine learning and AI signals.
• Collaborate with Product, Machine Learning, Analytics, and Fraud Strategy to weigh risks and trade-offs.
• Support operations and system availability through metrics, escalation, and on-call duties.
• Foster a culture of quality and ownership by setting code review and design standards and mentoring teammates.

This job description is not a contractual document and is not intended to have binding force. The role is remote within Poland; the majority of Affirm roles are remote and can be located anywhere within the country of employment. Affirm provides reasonable accommodations for candidates with disabilities during the hiring process.