Senior Software Engineer (Backend) – Fraud

As a Senior Software Engineer (Backend) at BVNK, you'll design and build the backend systems that detect and prevent fraud across the whole customer journey: onboarding, login and account activity, payments and card transactions. You'll bring device, behavioural and transaction signals together, power real-time risk decisions, and equip the Fraud Operations team with the data and tools they need to act quickly. Working in a small, autonomous squad that owns its problem space, you'll help build a fraud prevention capability from an early stage at a company moving money across fiat, crypto and card rails at global scale.

What you'll do

• Design, build and maintain secure, scalable backend services and APIs that power fraud detection, risk decisioning and controls.
• Build low-latency services that assess risk and approve, decline or challenge activity in real time, including card authorisations and payments.
• Ingest and enrich device, session, behavioural and transaction data, and integrate it with third-party fraud and risk providers to build a full risk profile.
• Build risk-based controls such as limits, velocity checks, blocks and step-up challenges (e.g. MFA or liveness) that stop fraud while keeping legitimate customers moving.
• Deliver the data pipelines, metrics and alerting that let the business measure fraud, tune rules and respond quickly to new attack patterns.
• Work with data and ML colleagues to put machine learning models and AI-assisted workflows into production.
• Work with Fraud Operations, Financial Crime, Cards, Payments and Data teams to deliver features end to end.
• Contribute to architecture decisions, review code, mentor other engineers and help shape the engineering culture of a growing team.
• Own your services in production, including monitoring, incident response and continuous improvement of reliability and performance.

What you bring

• Strong, proven experience as a backend engineer building production systems in Java with Spring Boot.
• Hands-on experience with microservices and event-driven architectures, ideally with Kafka or similar messaging platforms.
• Experience building systems where low latency, correctness, idempotency and auditability matter.
• Comfort working with large volumes of event and transaction data, and building pipelines that turn raw signals into decisions and insight.
• Experience integrating with third-party APIs and webhooks, including handling failures, retries and data quality.
• Experience with cloud platforms (preferably AWS), containerisation and CI/CD pipelines.
• A solid grasp of secure coding practices and handling sensitive data in regulated environments.
• Ownership of outcomes, clear communication with technical and non-technical stakeholders, and comfort in a fast-moving environment where you're building from scratch.
• Use of AI tools and agentic workflows to speed up delivery and improve quality.

Nice to have

• Experience building fraud detection, transaction monitoring, risk scoring or account takeover prevention systems.
• Experience with rules engines or putting ML models into production for real-time decisioning.
• Experience with card authorisation flows, 3DS, chargebacks or payment rails such as Faster Payments, SEPA or ACH.
• Experience with stablecoins, crypto or blockchain-based payments.

What we offer

• Competitive salary: Bulgaria €70,000-€110,000 EUR, Spain €85,000-€110,000 EUR, Poland 250,000-480,000 PLN (based on experience and relevant certifications)
• Flexible working hours with hybrid working at its core
• Flexible approach to holiday
• Opportunities to travel to offices around the world

About BVNK

BVNK is the stablecoin-powered financial stack for enterprises, now part of Mastercard. Operating across 130+ countries with 40+ licenses for fiat and digital assets, BVNK enables businesses to build financial products, unlock new markets, and move money in seconds. Trusted by industry leaders like Corpay, Worldpay, Deel, and Flywire, BVNK delivers the infrastructure that makes new forms of money usable within the financial systems customers already rely on.