Senior Software Engineer, Back-end – Fraud

Affirm

Senior Software Engineer developing real-time fraud decisioning systems for Affirm. Collaborating with North American teams to enhance software in the fintech space.

Posted 7/20/2026full-timeRemote • 🇪🇸 SpainSenior💰 €86,000 - €122,000 per yearWebsite

Core Competencies

Role fit

Core Competencies

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Demonstrates expertise in building scalable backend systems using Python or Kotlin, with a strong focus on system design, AI-driven engineering, and operational excellence. Proven ability to lead teams through ambiguity, fostering a culture of quality and ownership while collaborating across product development lifecycles.

Highest-signal resume keywords

Python Backend DevelopmentKotlin Backend DevelopmentAWS InfrastructureDistributed Systems DesignAI-Driven Engineering

ATS Keywords

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Applicant Tracking System Keywords

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Hard Skills

Backend Systems DevelopmentSystem DesignSQL ProficiencyCI/CD PracticesReal-Time Decisioning

Soft Skills

Strong Communication SkillsProactive MindsetTeam CollaborationMentoringOwnership-Driven

Tools & Technologies

MySQLPostgreSQLKubernetesSnowflakeAirflow

Industry Keywords

Fraud PreventionRisk SystemsFintech SectorComplianceInternationalization

Tech Stack

Tools & technologies

AirflowAWSDistributed SystemsKotlinKubernetesMySQLPostgresPythonSQL

About the role

Key responsibilities & impact

You will 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.
You will 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.
You will 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.
You will 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.
You will 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.
You will 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.
You will foster a culture of quality and ownership - setting and improving code review and design standards, mentoring teammates, and leading by example.
On-Call Rotation - There would be an on-call rotation for this role as a requirement.

Requirements

What you’ll need

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)

Benefits

Comp & perks

100% subsidized medical coverage, dental and vision for you and your dependents
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