Senior Software Engineer (C#)

CompanyNMI

LocationUnited Kingdom

Posted At11/13/2025

UK Visa Sponsorship Analytics

Occupation Type

Programmers and software development professionals

Occupation Code Skill LevelHigher Skilled

Sponsorship Salary Threshold

£54,700 (£28.05 per hour)

Occupation rate applies

Above analytics are generated algorithmically based on job titles and may not always be the same as the company's job classification. You can also check detailed occupation eligibility, and salary criteria on our UK Visa Eligible Occupations & Salary Thresholds page.

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Description

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.

We are seeking an experienced Software Engineer to join our Payments Processing group. This group focuses on developing and maintaining world-class payment solutions, including PIN pad and card reader integration and processor/acquirer connectivity.

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

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.

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 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, 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

£48,000—£60,000 GBP