Backend Software Engineer - Golang or Java - Lisbon/Berlin Based

About this role

About Us 1GLOBAL is a technology-driven global mobile communications provider, delivering global connectivity solutions to enterprises and consumers. Powered by a best-in-class telecom platform with its own owned and operated global mobile core network in 15 countries, fully fledged in-house developed eSIM technology, and an extensive portfolio of telecom licenses; 1GLOBAL operates as a fully regulated telecommunications provider across 43 countries worldwide. The company serves many of the world’s leading banks, multinational enterprises, global retailers and digital-first businesses, including neo-banks, global fast moving consumer goods companies, travel leaders, and payment service providers. Today, 1GLOBAL connects more than 80 million people and devices globally, enabling our customers to launch, scale, and innovate with confidence in the mobile ecosystem. 1GLOBAL is a profitable, fast-growing business. With full-year revenues in 2025 exceeding US$200 million and profits of over US$25 million, we generate strong cash flows to fund our growth allowing us to continuously invest in infrastructure, platform innovation, and global expansion. In 2026 also the parent of the Lidl Group acquired a 10% interest in 1GLOBAL as part of a deal for Lidl to offer globally to its 180 million consumers communication services. Recent years have marked a defining phase in 1GLOBAL’s journey, with major enterprise and mass-consumer client wins accelerating its evolution into a global mobile connectivity powerhouse, purpose-built to enable consumer brands to enter and succeed with their own aspirations to offer telecommunications services to their clients. Founded in 2022 by experienced technology entrepreneurs, Hakan Koç and Pyrros Koussios, 1GLOBAL has rapidly emerged as a European technology leader shaping the future of global telecommunications. It operates as a fully regulated Mobile Virtual Network Operator (MVNO) in 15 countries and as a regulated telecom operator in an additional 28 markets. Headquartered in the Netherlands, with world-class R&D hubs in Lisbon, Berlin, and São Paulo, its team of close to 550 experts across 16 countries is united by a single ambition: to redefine global mobile connectivity through technology, scale, and execution excellence. About the Team You will be joining a dynamic team at the forefront of developing and maintaining our Network API, xSIM Management System, and Recording Platforms. The Network API powers critical systems and services that enable the creation, configuration, and real-time monitoring of subscriber configurations across a wide array of business scenarios. These include enterprise solutions, IoT deployments, regulatory compliance, and recording services, ensuring seamless connectivity for everyone and everything. Our xSIM Management System is a high-performance, low-latency platform designed to handle hundreds of transactions per second, keeping all xSIMs accurately updated in real time. Meanwhile, our Recording Platforms deliver robust Mobile Compliance & Recording capabilities tailored for financial institutions, automatically capturing client and employee interactions either on-premises or through our secure cloud infrastructure. We run a multi-site platform, following strict security requirements, provide the service to customers around the world and manage millions of subscriber profiles. We embrace a highly collaborative and diverse environment, value teamwork, autonomy and hold ourselves accountable for our deliverables and customer success. About the Role Provide accurate effort estimates to support roadmap planning and effective expectation management Design and implement resilient, scalable, secure, and fault-tolerant architectures to ensure system reliability and performance Develop new features and support existing systems across the Network API, xSIM Management System, and Recording Platforms Contribute with small, incremental enhancements that seamlessly integrate into the established codebases Maintain and update existing solutions to keep them modern, efficient, and reliable Collaborate with team members to ensure smooth development processes and shared understanding Write and maintain comprehensive tests to ensure fast regression and reliable validation of new features Implement procedures and metrics to enable effective monitoring and observability of platform contributions Participate in code reviews to promote high standards of code quality, readability, and maintainability Take ownership of the quality and outcomes of your work, ensuring fully functional end-to-end flows Create and maintain accurate, up-to-date technical documentation Actively contribute to team discussions, with a mindset for continuous improvement and openness to new ideas or technologies Requirements About You Must-haves 6+ years of professional experience in backend development, preferably with Go (Golang). Strong Java experience with willing to learn Go is also welcome Strong understanding of concurrency models, with practical experience in implementing asynchronous workflows, inter-process communication, and synchronisation techniques Skilled in designing, building, and consuming RESTful APIs, following best practices for API design and performance optimisation Proven experience working with databases, both relational (e.g., PostgreSQL) and non-relational (e.g., Redis, MongoDB, DynamoDB), including data modelling, query optimisation, and performance tuning Experienced in writing unit tests, integration tests, and benchmarks, with a test-driven development mindset Comfortable with networking protocols and distributed communication patterns (e.g., gRPC, WebSockets, TCP/UDP) Experienced in building scalable microservices architectures and distributed systems Knowledgeable in applying software engineering best practices and design patterns for maintainable, testable code. Skilled in using DevOps tools and practices, including Docker, CI/CD pipelines, and Infr