(Senior) Full-Stack Software Engineer - Financial Infrastructure & Payments (m/f/d)

1KOMMA5° At 1KOMMA5° , we pursue a clear vision: Living on wind and sunlight forever for free . To make this a reality, we are building the energy system of the future with Heartbeat AI. Want to be part of it?We bring together regional craftsmanship and scalable software: We don't think of solar, batteries, heat pumps, and e-mobility as isolated components, but control them as an intelligent, integrated overall system in our virtual power plant. Directly connected to the electricity market – in real time, fully automated. This way, energy is used when it is available from renewables and particularly cost-effective. By 2030, our goal is to transition 1.5 million households to renewable energies. Over 3,000 people are working towards this every day, at more than 80 locations worldwide, from Finland to Australia. Want to take responsibility and build solutions that truly matter? Apply now and help us shape the energy world of tomorrow. Learn about our Product & Tech team! Deine Position You architect the billing , invoicing , and monetization systems behind the global energy transition, one unified internal platform. By designing and running everything from invoicing and subscriptions to PSP-backed payments and reconciliation, you make sustainable energy financially solid and operationally scalable. The audit trails, templates, and integrations you build are what finance teams and customers trust as we grow across markets. As a Software Engineer at 1KOMMA5° , you will take technical ownership of key systems and features, driving architectural decisions and ensuring scalability, reliability, and performance. You’ll collaborate closely with other engineers, product managers, and stakeholders to shape our technical direction and deliver high-impact solutions. Beyond building solution, you’ll mentor teammates, champion engineering excellence, and help evolve our development and deployment practices to the next level. Key responsibilities include but are not limited to: Contribute as a Full-stack engineer within a team of self-driven software developers Design, build, and maintain business-critical systems across the stack. From scalable backend services and APIs to performant, user-friendly frontends with reliable flows for invoices, payments, and subscriptions where they touch customers and finance Partner with finance, operations, and product to translate complex, loosely defined billing requirements into clear, actionable technical solutions , including compliance-minded documents and audit-friendly reporting where needed Own slices of the invoice lifecycle (generation, delivery, and archival), templating and localization , and reconciliation and reporting together with stakeholders Champion clean architecture , component reusability, and maintainable UI patterns using modern frameworks (e.g. React, Next.js, or similar) Drive experiment-driven innovation and uphold strong engineering practices in testing, CI/CD, observability, and code quality Continuously improve developer experience by reducing technical debt, automating workflows, and documenting key decisions and operational processes Operate effectively in an asynchronous, outcome-oriented environment , managing your work autonomously and maintaining clear communication through documentation and structured updates Contribute to lightweight project management by defining milestones, ensuring technical feasibility, and aligning engineering work with product goals Our Stack: TypeScript / JavaScript Next.js for frontend applications NestJS and for backend applications and APIs Postgres, Auth0, OpenAPI Infrastructure as code Deployment to Google Cloud/Vercel Observability with Datadog Dein Profil Experience writing maintainable, reusable, and testable code in TypeScript , with strong skills in both frontend frameworks and backend technologies Strong understanding of API design , data modeling, and system integration (RESTful or GraphQL), including patterns for idempotent money mov