Full-Stack Developer – API Integrations & Analytics Web Platform

Hi! ???? We are a growing European media & e-commerce agency looking for a **talented and reliable Full-Stack Developer** to build a custom API-based web application with us. This starts as a focused project but has strong potential to become a **long-term development partnership** with ongoing work and new features. We are looking for someone who enjoys solving technical problems, thinks about architecture before coding, communicates openly, and takes responsibility for the quality of their work. Full project details will be shared with shortlisted candidates. ## What You Should Be Good At The project involves connecting multiple external platforms, synchronizing and storing data, and displaying it in a multi-client web application. Strong experience in several of the following areas is important: * REST APIs & third-party API integrations * OAuth 2.0 & token refresh * PostgreSQL * Multi-tenant architecture * Background jobs / scheduled data synchronization * Data normalization & historical data storage * Secure authentication * Role-based access control * API rate limits, retries & error handling * React / Next.js * Node.js / NestJS or Python / FastAPI * Git / GitHub * Cloud deployment Experience with APIs such as **Shopify, Meta/Instagram, TikTok, Amazon, Pinterest or Google** is a strong advantage. ### Backend quality is more important than fancy design. The frontend should initially be clean and functional. However, it must use **reusable components and a well-structured frontend architecture**, so that a professional Figma/UI design can easily be implemented later. ## How We Want the Application to Work At a high level, we are looking for an architecture similar to: **External APIs ? Background Synchronization ? Data Storage / Normalization ? PostgreSQL ? Backend ? Web Dashboard** We do **not** want external APIs to be queried every time a user opens the dashboard. The application will eventually contain multiple clients, so proper and secure **tenant separation** is essential from the beginning. The architecture should also make it easy to add additional API connectors later without rebuilding the entire system. ## Technical Questions Please answer the following questions **briefly and in your own words**. Specific answers based on real experience are much more valuable to us than long textbook-style answers. **1.** You need to collect analytics data from five different external APIs. Would you call all five APIs whenever a user opens the dashboard? If not, how would you structure the system? **2.** A scheduled synchronization suddenly receives repeated HTTP 429 responses. What is happening and what would your application do? **3.** An OAuth access token expires while a background synchronization is running. How would you handle this? **4.** Twenty clients use the same application. How would you make sure Client A can never access Client B's data, even if someone manually modifies an API request? **5.** API A calls a metric `spend`, API B calls it `cost`, and another API provides the value in cents. How would you design the data layer so the application can work with one consistent metric? **6.** An API only provides the current follower count, but the application needs to show follower growth over the last 90 days. How would you solve this? **7.** Tell us briefly about the most difficult third-party API integration you have personally built. What made it difficult and how did you solve it? **8.** Which technology stack would you choose for this project and why? We may discuss your answers during a short interview. ## Paid Technical Trial – $65 Fixed Budget Shortlisted candidates will be invited to complete the same small **paid technical trial project**. **Fixed trial payment: $65 USD** The trial is intentionally limited in scope and should take an experienced developer approximately **6–8 hours**. The trial will use a real e-commerce use case with restricted access to one