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# Senior Backend Engineer

- **Company:** Payflows
- **Location:** Paris, France
- **Experience:** Expert
- **Contract:** Permanent contract
- **Skills:** Application Programming Interfaces (APIs), Artificial Intelligence, Amazon Web Services, Code Review, Python (Programming Language), PostgreSQL, Backend, Agentic-AI, Fastapi, Front End Software Development, Code Restructuring, Serverless Computing
- **Published:** October 29, 2026
- **Apply:** https://www.welcometothejungle.com/en/companies/payflows/jobs/senior-backend-engineer_paris_PAYFL_wbb8bpo

## About the Role

* You like building products people actually use.
 * You are autonomous and take ownership of what you ship.
 * You take initiative and lead by example.
 * You're curious and enjoy figuring things out.
 * You're pragmatic about trade-offs.
 * You communicate with kindness and clarity.

## Description

* Design and implement new services for a product feature.
 * Refactor an early service to make it more robust.
 * Investigate a performance or production issue.
 * Work with product and frontend to shape a new feature.
 * Review code and help teammates improve.
 * Build backend tools that our AI agents use to perform real finance operations.
 * Design safe, deterministic workflows where agents propose actions and humans review them.

Your time will be split between building new features and improving what already exists. Both matter.

You won't just build endpoints. You'll help shape the execution layer that our agents rely on: the APIs, data models, and workflows that let them act safely in production.

You'll work closely with product, frontend, and customer-facing teams. We expect engineers to take ownership of parts of the system and help make them more reliable over time.

Our current tech reality

Our stack evolves based on our challenges, but we care more about good design than trendy tools

Python is our core language. It helps us move fast, keep the code readable, and fits naturally with our AI-driven approach. A growing part of the system is built around agents that use our backend as a set of reliable, deterministic tools.

 * Core language: Python
 * Backend: FastAPI + Pydantic
 * Data: PostgreSQL
 * Infra: AWS, serverless when it makes sense
 * Performance: some Rust for critical paths
 * Architecture: multi-service backend, simple enough to reason about

Some parts of the system are clean and well-tested. Others were built quickly and need love. That's the phase we're in.

Over the next year, we'll focus on:

 * Turning core workflows into reliable tools for our agents
 * Simplifying services
 * Improving tests and observability
 * Making performance more predictable
 * Cleaning up early code