Senior Software Engineer
Senior Software Engineer (Payment Gateway) | Kotlin
Up to £650/day | Inside IR35 | Hybrid London (3 days onsite) | 6 months initial
A major UK financial institution is rebuilding their payment gateway from scratch. Not patching the old one. Not migrating. A clean greenfield refactor of one of the most significant payment infrastructures in the country.
The names processing through this system tell the story. The Q3 MVP is already pulling forward. The team is scaling fast. Three weeks into discovery and the momentum is already there.
This is a senior engineering role for someone who has actually built payment gateways, not just integrated into them. You'll be the domain expert on a high-visibility programme, working alongside a premium FS engineering consultancy to design the system that will process payments across in-person and digital channels at serious scale.
The technical environment is Kotlin-first, with a preference for engineers who have lived in the JVM ecosystem and can move quickly with modern tooling. The architecture challenge spans high and low level design, merchant onboarding, payment processing flows and POS integration. TDD matters here. So does the ability to operate confidently in a regulated banking environment.
Beyond the code, you'll be taking high-level requirements and turning them into structured backlogs, making architectural decisions that will shape the platform for years, and having senior stakeholder conversations that require both credibility and composure. This isn't a role for someone who wants to keep their head down.
Engineering culture is driven by a consultancy delivery model: high expectations, low ego, commercially aware. The kind of environment where strong technical opinions are expected and challenged in equal measure.
You'll enjoy this if you:
- Have strong Kotlin or JVM experience and are comfortable going full stack with React
- Enjoy greenfield builds where you're shaping architecture from the ground up
- Can take ambiguous, high-level requirements and turn them into structured, deliverable backlogs
- Have led or mentored engineers and are comfortable owning technical decisions
- Want to work on a high-visibility programme at a Tier 1 banking client
- Are happy operating in a regulated environment with senior stakeholder exposure
6 months initial with strong extension likelihood. The programme is growing and Q3 is a hard target.
Curious? Hit apply or drop me a message directly. Happy to talk through the detail informally before you commit to anything.