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Senior Software Engineer, Back-end (Fraud)

Affirm· Checkout
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Hybrid (Spain)€86k - €122kFull-timePosted 3mo ago

About the role

Senior backend engineer role focused on real-time fraud decisioning systems and regional expansion (internationalization) for Affirm's Fraud Decisioning System, collaborating with product, ML, analytics, and fraud strategy across Europe and North America.

Responsibilities

  • Own and deliver quarterly goals for the team, leading engineers through ambiguity and supporting delivery.
  • Design and implement real-time fraud decisioning services and APIs in Python or Kotlin, extending the Fraud Decisioning System to markets beyond the US.
  • Build and evolve platform and tooling to launch fraud decisioning in new countries quickly, turning market setup into a repeatable, scalable process.
  • Integrate region-specific fraud and risk vendors and operationalize ML/AI signals powering real-time decisioning; use AI tooling to accelerate engineering work.
  • Support peers and stakeholders across the product lifecycle, articulating constraints and balancing risks and trade-offs.
  • Maintain operations and availability of team systems by creating/monitoring metrics, escalating issues, and contributing to on-call readiness.
  • Foster a culture of quality and ownership; set/advise on code review and design standards; mentor teammates.
  • Participate in on-call rotation as a requirement.

Qualifications

  • 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.
  • Proficiency with AI-driven engineering practices and ability to review and critique AI-generated code (Claude Code/AI tooling).
  • Proficiency in SQL and working with 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 with focus on learning and team success.

Skills

Required:Backend development (Python/Kotlin)Distributed systemsAWSMySQL/PostgreSQLKubernetesSQLCI/CD

Benefits

  • Health coverage at no cost for employees and dependents.
  • Monthly stipends for tech setup and health/wellness options.
  • Flexible time off and generous holiday calendars.
  • Employee stock purchase plan (ESPP) with stock discount.
  • Spending stipends for tech, food, and lifestyle.
  • Parental benefits.
  • Learning & Development programs.
  • Away Days - wellness days.
Last updated Sep 16, 2026. Interested? Apply on the company site.

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