Job Description

Date Posted: 3rd March 2019

Date Ending: Ongoing (Previously 31st March 2019)


  • Job Title: Backend Developer - Senior
  • Salary range: £75k to £90k plus equity
  • Permanent position
  • Reporting to the CTO
  • London Office: 2nd Floor, Aldgate Tower, 2 Leman Street, London, E1 8FA

No. More. Paper. Receipts!

We're building the world's first API to tell you exactly what you've bought, not just how much you've spent. We are looking for a talented developer with a passion for API's and microservices who is excited at the opportunity to be involved with everything between feature planning, implementation, testing and architecture of a best in class system.

See our Life at Flux video to learn more about working at Flux:

Our engineering team are deeply curious and phenomenal problem solvers. We are building a revolutionary platform that is on the cutting edge of technology and financial regulation. As an engineering team we all work very closely with all parts of the business including legal, product, sales and operations. We don’t believe in working in silos and make sure people are mixed up, starting with where you physically sit at our headquarters in Aldgate East, London. There is no dark corner just with engineers!


  • Retailer and bank API integrations
  • Matching Algorithm, find and implement improvements to our matching algorithm that will allow throughput of millions of transactions per day
  • Build out Blueberry, Flux's merchant dashboard which processes complex analytics over large data sets in real time. This involves development of a GraphQL service that serves these stats and other data over websockets
  • New product development (e.g. displaying nutritional info via receipts, building a better returns process for retailers or improving our developer experience)

Tech Stack:

Our tech stack follows open standards and handles a large volume of transactional data from some of the biggest retailers and banks in the UK. These are processed in microservices. Our backend is written in Kotlin which is based on the JVM and our frontend is primarily in React. We use GraphQL and subscriptions to facilitate real time communication between the frontend and backend and deliver analytics to our retailers in retailers. The infrastructure is built using Docker and Kubernetes.

Interview Process:

The interview process will include an interview where we will walk you through a coding case study and an architecture case study. This is to test that your ability to synthesise, analyse and provide solutions is at the relevant level required for this role.


  • You have at least 2 years commercial experience in backend software development
  • You have at least 2 start up/greenfield experiences (experience working in an agile teams building complex systems from scratch)
  • You have extensive experience in 2 programming languages with 1 being a JVM language (e.g. Kotlin, Java, Scala etc)
  • You have in depth experience designing and delivering low latency, highly scalable complex systems which consume large amounts of data
  • You have excellent communication skills with both engineering and business people to support and deliver cross departmental projects
  • You can demonstrate a passion for technology and engineering through relevant extra curricular activities e.g. side projects, blogs, engagement with wider tech community.


  • Generous holiday allowance (28 days) - we encourage everyone to use their allowance!
  • Join the Flux Club! £100/month spending money at Flux Retailers (EAT. pod, itsu, Pure, KFC)
  • Company pension scheme
  • Weekly team lunches
  • Annual company trip
  • Work from home Wednesday (after 3 months) and Fridays
  • Central London location Aldgate East
  • Unlimited artisan coffee
  • Fresh fruits, nuts, beers and other snacks provided
  • Latest Macbook Pro, screen and additional tech set-up required
  • Office building perks such as weekly yoga and fitness classes
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