FIX Onboarding & Client Services, EMEA

Hybrid, London, UK (3+ days per week in-office) | Full-Time

About Us

Reactive Markets is the 2026 OTC Trading Platform of the Year (Risk.net). Our network handles over $75 billion in daily trading volumes across FX, Equities, and Cryptocurrency, connecting 60+ of the world's leading liquidity providers.

We build trading systems that operate at the edge of what's technically possible — where nanoseconds matter and a dropped message costs real money. Our engineering team is small, senior, and deeply invested in the craft of building cutting edge, reliable, high-performance systems.

The Role

We are seeking a motivated and technically curious Onboarding and Client Services professional to join our London team. This role will focus on FIX client onboarding, integrations, and client service delivery across FX, equities and digital assets. The successful candidate will work closely with clients and internal teams to ensure seamless connectivity, smooth integration, and exceptional service throughout the client lifecycle.

We're building genuinely AI-enabled tooling to support this function — so this role is less about arriving with a decade of FIX expertise already committed to memory, and much more about someone sharp, adaptable, and genuinely curious who can use that tooling to go further, faster, and think proactively about how the process itself should keep improving.

What You'll Work On

FIX Onboarding & Integrations

Lead and manage FIX client onboarding projects — from initial requirements gathering through certification and production go-live.

Configure, test, and validate FIX sessions, including order routing, execution reporting, and market data flows.

Coordinate conformance testing and certification with clients to ensure compliance with platform standards.

Document onboarding procedures, client configurations, and integration best practices.

Leverage internal AI and automation tools to streamline client onboarding and troubleshooting — including tooling built specifically for this function, giving you a genuine head start on deep process knowledge.

Collaborate with engineering and product teams to support new FIX workflows, APIs, and client integration initiatives.

Client Services

Serve as frontline technical support for clients in EMEA across FX and equities business lines.

Build and maintain strong client relationships, ensuring timely and transparent communication addressing their needs and queries with professionalism and efficiency.

Provide ongoing technical and operational support for production trading environments.

Manage client inquiries, troubleshoot workflow or configuration issues, and coordinate resolutions across internal teams.

Partner with account management, sales and product teams to ensure a positive client experience and successful delivery of platform enhancements.

What We Need

2-5 years of experience in a client onboarding, integration, or technical support role within financial technology, trading, or brokerage.

Good working knowledge of the FIX protocol — message structures, session management, and common trading workflows.

Genuine comfort troubleshooting FIX connectivity, analysing logs, and resolving integration issues, with the judgement to know when to dig deeper.

Familiarity with FX and Equities trading environments, order lifecycle management, and market data connectivity — genuine interest in working across multiple asset classes rather than staying within one.

A genuinely proactive, tech-first mindset — someone who treats our AI and automation tooling as a way to go further and faster, not a replacement for good judgement, and who naturally looks for ways to improve a process rather than simply following it.

Excellent communication and organisational skills, with strong attention to detail and the ability to manage multiple onboarding/client projects in parallel.

Nice-to-have

Experience with OMS/EMS platforms, liquidity aggregators, or trading system integrations.

Exposure to other API protocols and architectures (REST, WebSocket) — relevant given the depth of our own API.