Onboarding & Client Services Associate

FIX Onboarding & Client Services, EMEA

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

Reactive Markets is the 2026 OTC Trading Platform of the Year (). Our network handles billions in daily trading volumes across FX, Equities, and Cryptocurrency, connecting 35+ 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 reliable, high-performance systems.

We are seeking a motivated and technically skilled Onboarding and Client Services Associate 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.

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

Client Services

• Serve as a 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.

• 3+ years of experience in a client onboarding, integration, or technical support role within a financial technology, trading, or brokerage environment.
• Strong working knowledge of the FIX protocol — message structures, session management, and common trading workflows — with the ability to actually explain why a given configuration or workflow serves the client's business outcome, not just execute it.
• Proven experience troubleshooting FIX connectivity, analysing logs, and resolving integration issues.
• 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.
• Comfortable with (or curious about) automation and AI-assisted tooling in an operational context — this role uses internal AI/automation to streamline onboarding and troubleshooting, so a mindset that embraces efficiency over manual repetition matters more than any specific tool.
• 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, Web Socket) — relevant given the depth of our own API.
• Scripting or automation experience (e.g. Python) and familiarity with monitoring tools (Splunk, Grafana, or similar).
• Understanding of financial market structure and post-trade workflows.

• A genuinely rich API to work with — not a thin FIX wrapper bolted onto a legacy system. You'll onboard clients onto an API with real depth across order routing, execution reporting, and market data — the kind of platform where understanding the…