Senior Software Engineer

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.

We are seeking an experienced Software Engineer to join our Payments Processing group. You will design, develop, and maintain SDKs and backend components that enable secure, performance‑ready, and seamless payment transactions across payment device integrations.

• Design, develop, and maintain secure, scalable, high‑quality SDKs and backend services for 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 code and systems adhere to strong security and compliance requirements (PCI, OWASP).
• Investigate and resolve performance issues across SDKs and backend services.
• Contribute to cross‑team initiatives, including SDK standardization and shared libraries.
• Participate in out‑of‑hours on‑call rota to support critical product alerts.

• 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 object‑oriented design principles and software architecture knowledge.
• Deep understanding of the 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 (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 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 and proactive issue resolution.
• Excellent communication skills, capable of explaining complex technical concepts to both technical and non‑technical stakeholders.

• Annual bonus scheme dependent on individual and company performance.
• Annual salary of £48,000‑£58,000.
• 25 days holiday each year (plus bank holidays, with an additional day after each year of service up to 30 days).
• Private medical insurance after 30 days of employment.
• Remote‑first culture.
• Great work‑life balance with a Flexi‑time policy.
• Family‑friendly policies, including enhanced maternity and paternity pay and shared parental leave.
• Allocated company training budget.
• Bike‑2‑Work Scheme.
• Lifeworks Employee Assistance Programme offering wellbeing, family, and financial support services.
• Commitment to employee wellbeing, including mental health first aiders.
• Employee referral scheme with generous financial reward.
• Bonusly colleague reward scheme.

We are an Equal Opportunities employer and will provide reasonable support to applicants with disabilities. All offers of employment are subject to satisfactory background checks.

About NMI: NMI enables partners with choice and challenges the one‑size‑fits‑all approach to payments. We empower businesses to use the latest payment technologies securely and reliably.