NMI is excited to add a Senior Software Engineer to our growing team in the UK. This role sits within the Protocols team—responsible for building and maintaining mission-critical services that connect to card payment acquirers and processors. These systems, written primarily in C#, must be scalable, secure, observable, and highly available, ensuring seamless transaction processing for our global customer base.

The Protocols team is part of NMI's Payments Gateway group, which focuses on developing and maintaining world-class payment solutions, including PIN pad and card reader integration and processor/acquirer connectivity. As a Senior Engineer, you'll have a direct impact on how payments flow through the NMI platform, playing a key role in evolving our architecture and building scalable solutions. This role is ideal for engineers who thrive in dynamic environments, lead by example, and are eager to make critical systems more reliable, scalable, and maintainable.

Key Responsibilities

Contribute to the architecture of highly observable and fault-tolerant systems.
Lead technical discussions, participate in code reviews, and drive best practices in maintainability and performance.
Actively mentor and support the growth of junior team members.
Collaborate with cross-functional teams, including Product and QA, to ensure high-quality delivery.
Contribute to the evolution of our CI/CD pipelines and observability tooling.
Participate in the out-of-hours on-call rota to respond to incidents impacting payment flow.

Skills & Experience

Bachelor's degree in Computer Science, Information Technology, or equivalent experience.
Minimum of 5 years of experience developing complex software applications in a commercial environment.
Advanced proficiency in C# (preferred) or Java, with strong understanding of object-oriented design principles.
Deep understanding of the full software development lifecycle (SDLC) and agile methodologies.
Experience with relational databases (e.g., MySQL, SQL Server, Oracle).
Strong knowledge of security best practices (e.g. OWASP, PCI, SOC2, HIPAA).
Proficiency with Google Cloud Platform (GCP), Amazon Web Services (AWS), or similar cloud environments.
Demonstrated experience applying modern software development practices in a collaborative, agile environment.
Excellent communication skills, with a proven ability to mentor others and contribute to a strong team culture.
Experience with logging systems (such as Logz.io) and optimizing logs preferred.
Experience with containerization (e.g. Kubernetes, Docker, etc.) preferred
Experience with monitoring and alerting systems (e.g. DataDog, NewRelic, etc.) preferred.

As well as being a part of something exciting everyday, you will also receive the following benefits:

Annual bonus scheme dependent on individual and company performance
Annual salary of £47,000 - £57,000
25 days holiday each year (+ bank holidays + 1 day after each year of service with up to a max. of 30 days)
Workplace pension scheme
Private medical insurance (upon 30 days of employment)
7 hours per day, 35 hours per week
A remote first culture
Great work-life balance with our Flexi-time policy
Family Friendly policies (Enhanced Maternity and Paternity Pay and Shared Parental Leave).
A chance to develop with an allocated company training budget
Bike2Work Scheme
Lifeworks, an Employee Assistance Programme which offers wellbeing, family and financial support services, such as assessments, resources and even 1:1 counselling sessions. It also offers interesting perks such as discounts on gyms, restaurants, high street retailers and cinema tickets
A strong commitment to employee wellbeing including mental health first aiders
Employee referral scheme with generous financial reward
Bonusly colleague reward scheme

_We’re looking for creative and passionate people who share our vision of making payments easy. If that sounds like you and you meet the requirements above, then please click on 'Apply for this job'!

_We are an Equal Opportunities employer and will provide reasonable support throughout the recruitment process to applicants who have a disability. Please let us know in advance so that any support, aids or adaptations can be put in place to assist you.

Please be aware that all offers of employment are made subject to receipt of satisfactory background and financial checks.

About Us

NMI enables our partners with choice, and challenges the one-size-fits-all approach to payments. You've probably used NMI in the last 24 hours without even realising it. We’re the platform that powers success for innovative tech created by SMBs, entrepreneurs and fintech start-ups. We’re creative problem solvers who help visionaries smash through boundaries and think beyond what’s possible so they can think about what’s next. But we’re not just built for the tech savvy. We democratise the latest payments technology so that everyone can realise the benefits of easy payments across the full spectrum of commerce. We’re all about enabling more payments in more ways and more places.

Please note that in compliance with the data protection regulations within your jurisdiction, any personal information submitted with your job application may be collected and used by NMI for the purpose of recruitment and employment-related activities. By submitting your application, you acknowledge and provide explicit consent to the processing of your personal information as described in our privacy policy found on our website. For more information on how we process your information, please read our privacy policy here: https://www.nmi.com/legal/privacy-policy/

Salary Range, Depending On Experience

£47,000—£57,000 GBP