Back End Developer in London

Sientia is building the infrastructure that makes card-linked and Open Banking loyalty actually work at scale.

We sit at the centre of a network connecting the UK’s biggest banking and payments platforms - Revolut, Lloyds/Cardlytics, Monzo, Tide, Santander, British Airways and more - with brands who want to reach and reward real customers based on real spending behaviour, automatically, with none of the friction of traditional loyalty schemes.

It’s a fast-moving, high-growth corner of fintech, and we’ve built a genuinely differentiated position in it: strong publisher relationships, a growing Analytics/Intelligence product that turns transaction data into real commercial insight, and a client roster that includes some of the best-known brands in their categories.

We’re a small team moving quickly, with the ambition - and the traction - to become the category leader in CLO.

Anyone joining now is joining early enough to shape how that plays out.

About Sientia

Sientia is building the infrastructure that makes card-linked and Open Banking loyalty actually work at scale.

We sit at the centre of a network connecting the UK’s biggest banking and payments platforms - Revolut, Lloyds/Cardlytics, Monzo, Tide, Santander, British Airways and more - with brands who want to reach and reward real customers based on real spending behaviour, automatically, with none of the friction of traditional loyalty schemes.

It’s a fast-moving, high-growth corner of fintech, and we’ve built a genuinely differentiated position in it: strong publisher relationships, a growing Analytics/Intelligence product that turns transaction data into real commercial insight, and a client roster that includes some of the best-known brands in their categories.

We’re a small team moving quickly, with the ambition - and the traction - to become the category leader in CLO.

Anyone joining now is joining early enough to shape how that plays out.

Role Purpose

At Sientia the product is the infrastructure.

Everything we sell - attribution that actually reconciles, rewards that pay out correctly, intelligence a brand will act on - rests on backend services quietly doing the right thing with other people’s money and transaction data.

This role exists to help build and run those services, and to grow into owning more of them over time.

The Backend Engineer works on the systems that ingest transactions from banking and publisher partners, normalise and attribute them, and turn them into rewards, payouts and reporting.

You’ll start on well-scoped pieces of work with support and code review from the founders, and take on more end-to-end ownership as you build context and confidence.

This is a hands‑on role in a small team, which means real code shipping to a live fintech platform early - but it also means you’re never far from someone who can help.

We’re looking for someone at the start of their engineering career who is genuinely careful, curious, and quick to learn.

What you don’t know yet matters far less than how you approach not knowing it.

Key Responsibilities Backend development

• Build and ship backend features across our AWS estate - Lambda, API Gateway, Dynamo DB, S3/Cloud Front - in Node. js/Type Script, with support and review from the founders.
• Work on well-scoped tasks end-to-end: implement, test, and see them through to production.
• Learn our established services and our newer Type Script codebase, and help move work steadily toward the latter.
• Write code that’s clear and easy to review - favouring the boring and readable over the clever.
• Fixing, testing & quality
• Pick up bugs and smaller improvements across the platform, and use them to build a mental map of how the system fits together.
• Write and run tests, and check your own work carefully before it goes out - especially anything touching money or transaction data.
• Treat data correctness as something that matters: silent data loss, mis‑attribution and quiet filtering are the failure modes that hurt most here, and they rarely announce themselves.

Ask when a number looks wrong.

• Integrations & data pipeline
• Help maintain integrations with Open Banking providers, card issuing and payments partners, and reward fulfilment providers - learning how authentication, webhooks and retries work in practice.
• Help maintain the pipelines that ingest, normalise and classify transaction data from multiple banking and publisher sources, each with its own quirks and formats.
• Contribute clean, well‑shaped data that Analytics/Intelligence can build on.
• Automation & product feedback loop
• Automate small, manual processes that currently sit with Operations and the founders - reporting, reconciliation, invoicing checks, campaign setup - freeing up human time as we scale.
• Be another set of eyes on where the platform hurts: if something is confusing or broken while you’re working on it, say so.

Fresh perspective is genuinely useful feedback into a product.

• What Success Looks Like
• You’re shipping useful, reviewed changes to production within your first few weeks, and needing less hand‑holding each month.
• The work you take on gets done carefully - bugs you fix stay fixed, and your changes don’t create new surprises.
• You ask good questions early rather than getting quietly stuck, and you turn each answer into something you don’t need to ask twice.
• You handle money and transaction data with the care it deserves, and flag when something doesn’t look right.
• Six months in, you’re owning small features end-to-end and the team trusts your work.
• Candidate Requirements Essential
• Some hands‑on programming experience in a backend language - ideally Java Script/Type Script, but strong fundamentals in another language (Python, Java, Go, etc.) are fine.

This can be from a job, an internship, a bootcamp, a degree, or serious personal projects.

• Exposure to cloud platforms, especially AWS (Lambda, Dynamo DB, or similar)
• A real understanding of programming basics: how to structure code, work with data, call an API, and reason about why something isn’t working.
• Genuinely careful and detail‑focused - the kind of person who double‑checks their own work, especially where money is involved.
• Eager to learn, and comfortable saying “I don’t know that yet, but I’ll find out.” Curiosity and honesty matter more than knowing the answer.
• Clear communicator in writing - able to ask a good question, describe a problem, and work with non‑engineers (Operations, the founders) without disappearing into jargon.
• Reliable and proactive - asks for help early rather than going quiet when stuck.

Desirable (nice to have)

• Any interest in or exposure to fintech, payments, Open Banking, or card‑linked offers (CLO).
• Some experience with databases, APIs, or working with messy real‑world data.
• A public portfolio, Git Hub, or projects you can talk us through.
• Any exposure to a frontend framework (React) - this is a backend role, but curiosity across the stack is welcome.
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