Lead Backend Engineer (Java) | FlintN

Hi!

We are Boosta, a holding tech company that creates, develops, and invests in digital businesses with global potential. Today, we collaborate with over 800 specialists from different parts of the world, and millions of users use our products and services.

We are currently looking for a Lead Backend Engineer (Java) to join the FlintN to join Flintn, a business building and scaling an all-in-one payment platform for online businesses.

What you’ll be focusing on:

• Own the technical direction of one or more backend domains (payments, routing/cascading, subscriptions, chargebacks) - architecture, roadmap and technical debt strategy.
• Lead a team of backend engineers: task decomposition and planning, code review, mentoring, 1:1 technical guidance, onboarding of new hires.
• Design and drive delivery of distributed, high-throughput, fault-tolerant services and their APIs for internal teams and external integrations.
• Own service quality in production: SLOs, observability coverage, alerting, on-call rotation, incident response and postmortems.
• Own the release process for your domain - safe migrations, rollback-compatible changes, sandbox/production validation.

You are our ideal candidate if you:

• Have strong system design skills - able to own the architecture of a payment domain end-to-end: API contracts, data model, failure modes, idempotency, consistency guarantees, capacity and cost.
• Have deep Java (17/21) and Spring Boot 3.x expertise; are confident with concurrency, transactional boundaries, retry/backoff strategies and graceful degradation.
• Have production experience with event-driven architecture on Kafka - topic/partition design, ordering and delivery guarantees, consumer scaling, DLQ and replay, backward-compatible event evolution.
• Have advanced Postgres expertise - data modeling, indexing and query tuning, locking, zero-downtime and rollback-safe schema migrations (expand/contract).
• Have experience running services in Kubernetes/AWS (EKS, MSK, RDS, S3, IAM); are comfortable reading Terraform and Helm and reasoning about a GitOps delivery pipeline.
• Have experience with analytical/OLAP storage (ClickHouse, Opensearch or equivalent) - understand the trade-offs of a dual-path (OLTP + analytics) data flow.
• Treat observability as an engineering discipline: metrics, structured logs, distributed tracing, meaningful SLOs and alerts.
• Have strong payments domain expertise: authorize/capture/void/refund lifecycle, 3DS and challenge flows, chargebacks and disputes, PSP/acquirer integrations, routing and cascading, subscriptions and MIT/recurring billing, tokenization, PCI-DSS constraints.
• Have a practical security mindset - handling of card data, secrets management, least-privilege access, audit trails.
• Have ownership of engineering processes: code review culture, TDD/BDD, test pyramid (unit / integration / e2e), CI/CD, release and rollback procedures, incident management and postmortems.

Our hiring flow:

• Step 1: Pre-screen.
• Step 2: Technical interview with the CTO.
• Step 3: Interview with the CEO.
• Step 4: Reference Check.
• Step 5: Job Offer!

What you can expect from working with us:

• A chance to work on an early-stage payment product. You’ll have the opportunity to make architectural decisions, work with AI and high-level engineering, enjoy technical freedom, and directly influence the product’s development vector. The startup drive - backed by the stability and support of a holding company.
• From idea to action - minimal steps. Any proposal can turn into real changes in the product or processes. If you have an idea, it will be heard.
• Your office is wherever it’s convenient for you: home, our Kyiv office, coworking spaces in Lviv or Warsaw, or anywhere else with a stable Wi-Fi connection.
• Flexible working hours. Plan your day for maximum efficiency: start between 8:00 and 11:00 and finish between 17:00 and 20:00, considering team collaboration hours.
• Continuous growth is a must. Courses, conferences, and an internal library - we invest in your development because the team’s speed and performance directly depend on the expertise of its people.
• Health care and wellbeing: medical insurance, a Mental Health program, and compensation for sessions with a psychologist.
• Time to recharge: 28 paid days off per year, sick leave, and all public holidays fully covered.
• Gifts for special occasions. We celebrate important moments together - we give gifts to mark key milestones in your life and career.
• Social Impact. The Ukrainian Victory Support program and other charitable initiatives supporting Ukraine.
• An active corporate life: quarterly team buildings, workshops, and other holding-level events.

Our business ambition is to become one of the top 10 payment providers for small and medium-sized businesses. Are you in?