Staff Engineer - Global Billing, Payments & API

Location: London, Bristol or Edinburgh, UK (hybrid, three days a week in the office)

Level: Staff Engineer TL2

Team: Global Billing, Payments & API

Salary: £97,000 – £122,000 + discretionary bonus

Contract: Permanent

Reporting To: Senior Software Engineering Manager

Please note: This role requires an existing right to work in the UK. We can’t offer visa sponsorship, but we review sponsorship role by role, so keep an eye on our careers site for future opportunities.

About Kaluza

Kaluza is the Energy Intelligence Platform, turning energy complexity into seamless coordination. We help energy companies overcome today’s challenges while accelerating the shift to a clean, electrified future.

Our platform orchestrates millions of real-time decisions across homes, devices, markets and grids. By combining predictive algorithms with human-centred design, Kaluza makes clean energy dependable, affordable and adaptive to everyday life.

With teams across Europe, Asia and Australia, and a joint venture with Mitsubishi Corporation in Japan, we power leading companies including OVO, AGL and ENGIE, as well as innovators like Volvo and Volkswagen.

What you'll do

Kaluza runs the billing and payments engine behind some of the world's biggest energy retailers. This role builds and evolves the platform other engineering teams build on top of: the shared APIs, integration patterns, and technical standards that let billing and payments capability get built once and reused everywhere, instead of rebuilt separately for every new market or client relationship.

That matters because of where Kaluza is headed: as we grow into new markets and take on more of the world's largest energy retailers as clients, having a consistent, well-designed API platform is what lets new capability get adopted quickly and safely across every team that needs it, rather than each team solving integration and standards problems on its own. Getting this right directly shapes how fast Kaluza can extend billing and payments capability to new markets and clients.

We're also in the middle of reorganising how this part of the business works, moving toward one shared global core that every market configures rather than rebuilds. This role's remit, API platform and standards, is one of the technical foundations that shift depends on. Responsibilities include:

• You'll own system design and architecture for the API Platform and Standards squad, not just a single service.

• You'll create and challenge product and engineering proposals, backing design trade-offs with data.

• You'll diagnose and resolve complex technical and product issues, including in areas outside your immediate domain.

• You'll establish architectural patterns and technical standards that other teams build on top of.

• You'll take ambiguous, loosely-defined technical requirements and turn them into a concrete plan others can execute against.

• You'll influence engineering leadership, product, and adjacent squads to bring clarity and alignment on technical direction.

• You'll mentor and upskill engineers beyond your immediate team, contributing to a wider learning culture.

What you'll bring
Ideally you’ll have:

• Deep technical expertise applied to system design and architecture ownership across a squad, not just a single team or service.

• Be able to create and challenge product and engineering proposals and make design trade-offs, backed by data.

• A track record diagnosing and resolving complex technical and product issues, including in domains you aren't already close to.

• Be skilled at establishing and driving adoption of architectural patterns and technical standards that other teams build on top of.

• Be comfortable taking ambiguous, loosely-defined technical requirements and turning them into a concrete plan others can execute against.

• Be accomplished at influencing both upwards and outwards, bringing clarity and alignment to engineering leadership, product, and adjacent squads on technical direction.

• A track record mentoring and upskilling other engineers, and fostering a learning culture beyond your own immediate team.

• Be comfortable operating in a high-integrity data domain (billing or payments), where reliability, security, and auditability come before speed.

• Demonstrable customer obsession and a working-backwards practice: start from the problem other engineering teams or end customers have, and design the simplest platform capability that solves it.

• A demonstrable record of applying AI/LLMs to deliver customer impact, not just adopting AI tooling internally.

What will set you apart 

• Direct experience with API gateway, versioning, or developer-experience standards work at scale.

• Direct experience in billing, payments, or financial-services domains.

• Experience operating a "global core, configurable edge" or multi-market platform model (one engine, configuration at the edge, no client-specific forks of core logic).

Our Values

Five values guide how we work at Kaluza:

• Play to win: Collective pride in decarbonising energy at scale.

• Solve the real problem: Cutting through complexity to focus on real-world outcomes.

• Build trust every day: Consistency, transparency and doing what we say.

• Own the outcome: Full accountability, wins and setbacks, without ego.

• Go further together: Collaboration, respect and different perspectives.

Our Perks

• Time off and family: 26 days’ holiday, plus 26 weeks’ full pay for new parents with no qualifying service period

• Health and security: Private medical insurance with virtual GP, life assurance, pension scheme, free mortgage advice and eye tests

• Pay and flexibility: Discretionary bonus, a Flex Fund of 5% [of salary] to spend on the benefits you want most, retail discounts through Perks at Work

• Growth and setup: Personal learning budget, home office budget

• Climate: Furthr, our climate action app

Come as you are

We want to meet people from all walks of life. The more inclusive we are, the better our work will be, and we recognise talent on merit and potential. If you’re excited about the role but don’t tick every box, we’d still love to hear from you.

Find out more on our careers page and LinkedIn. Our Applicant Data Protection Policy is here.