Hi, I'm Sébastien 👋

API Integration Developer and API Customer Support

3 years debugging API integrations at Sellsy (3000+ issues resolved, 15 tickets/day, 98% customer satisfaction). Three years spent supporting API integrations at Sellsy have taught me one thing: most integration failures are predictable, optimizable, and avoidable. I am now ready to move from debugging other people's integrations to creating my own. I develop API integrations and connectors, and I share what I learn.

🔧 What I Do

• API Integration: REST APIs, OAuth, Webhooks
• Languages: Elixir, Node.js, Python, JavaScript
• Tools: Postman, Make, n8n,ActivePieces, Git, Docker

💼 Professional Experience

Sellsy (Feb 2022 - Present)

API Technical Support (2023 - Present)

• Support developers integrating with Sellsy API (15+ tickets/day, 3000+/year)
• Average staff satisfaction rate: 98% customer satisfaction
• Chift connector support (accounting tools connection)
• Key accomplishments: Identification and documentation of undocumented API V1 models. Contribution to more comprehensive and clearer FAQs. 20% reduction in recurring issues thanks to improved documentation and time savings in customer responses, e.g., the FAQ explaining how to make a V1 call using OAuth V2 is the most frequently used.

Software Developer (Feb 2022 - 2023)

• Backend/Frontend debugging (PHP, JavaScript, jQuery, XSL)
• Feature development (frontend)
• Legacy code maintenance and refactoring
• Developer integration import platform flatfile

🎓 Continuous Learning

• 275+ hours technical training (Dyma Academy)
• 8 certifications: Git, Python, Linux, Docker
• Mentored 80+ developers
• StackOverflow contributor I'm a passionate developer focused on creating technical solutions and exploring new technologies.

🔭 Current Projects

Anasto 🏗️

Multi-tenant integration platform for B2B marketplaces This repository aims to build a reusable node.js project base for establishing connections between different APIs.

• Multi-tenant architecture with PostgreSQL (1 schema/marketplace)
• High-performance REST API with Fastify + TypeScript
• Structured logging system with Pino
• JWT authentication and permission management
• Actively under development - Contributions welcome!

**tuSellsyApiV2

Unit testing an API in Elixir: useful for showcasing your skills in integration, business testing, and Elixir in an API/B2B context — worth mentioning if you want to demonstrate your expertise in API robustness/back-testing.

**Fast webhook listener

A super-fast Node.js microservice based on Fastify that listens to webhooks and pushes them into a Redis queue (via BullMQ) for asynchronous processing.

**Make_Filtered_rows

A concrete example of using the new Make module, which allows the use of JavaScript code. Here, filtering the sales lines of a Sellsy document get by API V2 to create a child document.

**AP_Sellsy_1

Another repository related to Sellsy: example of using Activepieces automation. This feature is not yet available in Sellsy but is coming soon.

🛠️ Core Stack

APIs: REST, OAuth, Webhooks
Languages: Elixir, Node.js, Python, JavaScript
Tools: Git, Docker, Make/n8n/ActivePieces, Ngrok Databases: PostgreSQL

(+15 years coding across 10+ languages)

StackOverFlow: @nseaSeb

28/10/2025

🎓 Continuous Learning

• 275+ hours of technical training completed (Dyma Academy)
• 8 professional certifications: Git, Python, Linux/Bash, Docker
• Mentored 80+ developers in the community

📫 How to Reach Me

• 🔗 GitHub: @nseaSeb
• 🌍 Location: Trizay, Nouvelle-Aquitaine, France 🇫🇷

🎯 Resources I've Created

• ElixirPhoenixRessources: Curated Elixir/Phoenix resources (French)
• clientsetchatiments: CSV/XLS manipulation tools in Python
• english_py:Python script for my own use that I am happy to share. Enables voice output of classic English phrases and voice recognition for pronunciation practice.

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Thanks for visiting my profile! Feel free to explore my projects and get in touch.