Senior Python Backend Developer (part-time / project) — German POS SaaS with Fiskal compliance

We need a senior backend engineer to help us harden and scale the codebase, add DATEV data Auto-Send, build the Subscription / Management portal, and prepare for the Fiskaly production go-live. About 15-25 h/week for 2-3 months, then either roll off or extend. Must have: - 3+ years Python/FastAPI in production - Solid MongoDB or PostgreSQL — multi-tenant patterns - One prior fintech / invoicing / POS project (any country) - Reads API vendor docs cold and ships Bonus points: - Prior work with fiskaly, DATEV, Elster, SEPA (pain.008), or German Fiskal software (orderbird / lexoffice / sevDesk / Gastronovi) - German language B1 - Frontend literacy (React/Tailwind) Send a short reply with: (1) a link to a similar project you shipped, (2) your take on how you'd approach a compliance bug in a live pod, (3) hourly rate + weekly availability. Applicants who just paste a portfolio without answering the 3 questions will be skipped. thank you.