Application Guide

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

at 1KOMMA5°

🏢 About 1KOMMA5°

1KOMMA5° is a fast-growing climate tech company on a mission to make buildings CO2-neutral by integrating decentralized clean energy, mobility, and heat supply solutions. They are building the digital backbone for the energy transition, offering a unique opportunity to work on impactful financial infrastructure at scale.

About This Role

This role focuses on architecting and building billing, invoicing, and payment systems that power the global energy transition. You'll own full-stack systems end-to-end, from scalable backend services to user-friendly frontends, directly impacting how customers pay for clean energy solutions.

💡 A Day in the Life

A typical day might start with a standup with your cross-functional team, followed by coding on a new invoice generation feature. You might then collaborate with finance to clarify a billing requirement, review a PR for a payment reconciliation service, and end the day by monitoring deployment of a hotfix for a payment issue.

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Interview Prep

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🎯 Who 1KOMMA5° Is Looking For

  • Strong TypeScript skills across both frontend (React, Vue, or Angular) and backend (Node.js, NestJS, or similar), with a focus on maintainable and testable code.
  • Deep understanding of financial system design: idempotent money movement, auditable billing events, reconciliation, and compliance-ready reporting.
  • Proven ability to own features end-to-end: from UX design and architecture to deployment, monitoring, and iteration based on feedback.
  • Excellent communication in English (German is a plus) and experience collaborating with cross-functional teams like finance and operations.

📝 Tips for Applying to 1KOMMA5°

1

Highlight any experience with payment service providers (PSPs), invoicing systems, or subscription billing platforms in your resume and cover letter.

2

Showcase specific TypeScript projects where you owned the full stack, especially those involving financial data or complex business logic.

3

Mention your understanding of idempotency, event sourcing, or audit trails in your application to demonstrate financial domain knowledge.

4

Tailor your portfolio or GitHub to include examples of clean API design, data modeling, or integration patterns (REST/GraphQL).

5

If you have experience with German tax or invoicing regulations (e.g., Umsatzsteuer), mention it explicitly—it's a strong plus.

✉️ What to Emphasize in Your Cover Letter

["Emphasize your passion for climate tech and the energy transition, linking your skills to 1KOMMA5°'s mission.", 'Describe a specific project where you architected a billing or payment system, detailing challenges and outcomes.', 'Showcase your ability to translate complex financial requirements into technical solutions, collaborating with non-technical stakeholders.', 'Mention your comfort with remote work and async communication, as the role is remote-first.']

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🔍 Research Before Applying

To stand out, make sure you've researched:

  • → Read about 1KOMMA5°'s product offerings: their energy management system, heat pumps, solar installations, and charging solutions.
  • → Understand the German energy market and regulatory landscape, especially for billing and invoicing in the renewable energy sector.
  • → Check their engineering blog or tech stack (e.g., if they use specific frameworks or cloud providers) to align your experience.
  • → Look up recent news or funding rounds to understand their growth stage and strategic priorities.

💬 Prepare for These Interview Topics

Based on this role, you may be asked about:

1 Design a billing system that handles recurring subscriptions and one-time payments with idempotency and audit trails.
2 How would you ensure data consistency across microservices in a payment reconciliation flow?
3 Walk us through a time you had to balance technical debt with feature delivery in a financial system.
4 How do you approach localization and templating for invoices across different countries?
5 Explain how you would monitor and alert on failed payment transactions in a production system.
Practice Interview Questions →

⚠️ Common Mistakes to Avoid

  • Don't submit a generic application without mentioning financial infrastructure or payment systems experience.
  • Avoid overpromising on skills you don't have—be honest about your experience with financial systems and TypeScript.
  • Don't neglect to show enthusiasm for the company's mission; they are likely looking for candidates who care about climate impact.

📅 Application Timeline

This position is open until filled. However, we recommend applying as soon as possible as roles at mission-driven organizations tend to fill quickly.

Typical hiring timeline:

1

Application Review

1-2 weeks

2

Initial Screening

Phone call or written assessment

3

Interviews

1-2 rounds, usually virtual

✓

Offer

Congratulations!

Ready to Apply?

Good luck with your application to 1KOMMA5°!

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