Senior Software Engineer (Remote, UK)

NMI is a leading provider of payment gateway solutions, specializing in card-present solutions and payment processing. Our innovative technologies empower businesses to securely accept payments and optimize transaction processes. With a focus on reliability, security, and innovation, we continuously push the boundaries of what’s possible in the payments industry.

The Ideal Candidate

The ideal candidate is a highly skilled software engineer with deep expertise in one or more of the following domains:

• Backend development (C#/.NET)
• Mobile SDK development for Android (Java/Kotlin) or iOS (Objective-C/Swift)

You don’t need to be an expert in all these areas, but you should bring senior-level technical depth and design experience in at least one, combined with the ability and curiosity to work across the stack when needed. As a Senior Engineer, you will play a key role in designing, developing, and maintaining SDKs and backend components that enable secure, performant, and seamless payment transactions. You will be expected to take ownership of complex problems, influence architectural decisions, and contribute to improving our CI/CD, testing, and deployment processes. You’ll also provide mentorship, participate in design discussions, and help ensure that our systems and SDKs meet the highest standards of security, reliability, performance, and maintainability.

Key Responsibilities

• Design, develop, and maintain secure, scalable, high-quality SDKs and backend services used in payment device integrations.
• Lead architectural and design discussions across backend and mobile platforms.
• Write and review well-structured, maintainable, and efficient code.
• Collaborate closely with Product, QA, and Operations to ensure successful feature delivery.
• Mentor junior and mid-level engineers, sharing best practices and guiding technical growth.
• Participate in the evolution of CI/CD pipelines and deployment automation.
• Ensure that all code and systems adhere to strong security and compliance requirements (e.g., PCI, OWASP).
• Investigate and resolve performance issues across SDKs and backend services.
• Contribute to cross-team initiatives, including SDK standardization and shared libraries.
• Join the team’s out-of-hours on-call rota to support critical product alerts.

Skills & Experience

• Bachelor's degree in Computer Science, Information Technology, or equivalent experience.
• Minimum of 5 years of experience in developing complex software applications in a commercial environment.
• Advanced proficiency in C# (preferred) or Java, with a strong understanding of object-oriented design principles and software architecture.
• Deep understanding of the Software Development Life Cycle (SDLC) and agile methodologies.
• Experience with relational databases (e.g., MySQL, SQL Server, Oracle) and optimizing database interactions.
• Strong knowledge of security best practices, including secure coding principles and compliance requirements (e.g., OWASP Top Ten, PCI, SOC2, HIPAA).
• Proficient in networking concepts such as sockets, HTTPS, DNS, and SSL.
• Deep knowledge of design patterns and their practical application.
• Proven ability to work independently while also fostering teamwork and cross-team collaboration.
• Demonstrated ability to mentor junior engineers and contribute to the growth of the engineering team.
• Strong problem-solving skills, with the ability to anticipate potential issues and proactively address them.
• Excellent communication skills, capable of explaining complex technical concepts to both technical and non-technical stakeholders.

Benefits

• Annual bonus scheme dependent on individual and company performance.
• Annual salary of £48,000 - £60,000.
• 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.
• 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. 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. We’re all about enabling more payments in more ways and more places.