Lago ( https://getlago.com/ ) | Hiring in Paris and remote in wider Europe and Americas for various roles | Hiring acros

The gap in what exists

While many billing solutions exist, there's a specific and growing need for 'AI-native' and usage-based billing platforms that can handle complex, flexible pricing models at scale, especially for startups and enterprises that want more control than off-the-shelf SaaS provides.

Wedge to win

Target AI/cloud infrastructure startups and scale-ups that need granular control over usage-based billing and want an open-source foundation, positioning against the high costs and black-box nature of proprietary solutions.

Reputation value (worth doing free for proof) — 70/100

Building a robust, open-source billing engine that handles complex usage metering would be a significant portfolio piece, demonstrating expertise in critical backend systems and finance tech.

Likely monetization

Open-source core, enterprise features/support, hosted SaaS

Incumbents to beat

Stripe Billing

You are a senior full-stack developer. Build an MVP for a simplified, open-source, AI-native billing platform similar to Lago. The MVP should focus on core metering and invoice generation for usage-based pricing. Use Next.js 16 App Router for the frontend, React 19, Tailwind v4 for styling. The backend should be a Node.js API (Express or Fastify) backed by Neon Postgres with a `pgvector` extension for future AI features (though not used in this MVP). The system needs to support a single customer with a single 'plan' that has one usage-based 'meter' (e.g., 'API calls').

MVP Requirements:
1.  **Customer Management**: Allow creation of one customer with basic details (name, email).
2.  **Plan Definition**: Define a 'plan' with a simple usage-based pricing model: e.g., '$0.01 per API call'.
3.  **Usage Event Ingestion API**: Create a secure API endpoint (`POST /api/usage`) that accepts JSON payloads representing usage events (e.g., `{ "customerId": "uuid", "meterName": "api_calls", "quantity": 1, "timestamp": "ISOString" }`). Authenticate this API with a simple API key.
4.  **Usage Tracking**: Store usage events in the Neon Postgres database, aggregated by customer and meter for the current billing period.
5.  **Manual Invoice Generation**: Implement an API endpoint (`POST /api/invoice/generate`) that, when called, calculates the total bill for the current period for the customer based on tracked usage and the defined plan, then stores a simple invoice record. The invoice should include total quantity for the meter and the calculated amount. Do not implement payment processing for the MVP.
6.  **Admin Dashboard**: A simple Next.js page where the operator can view the current customer, their accumulated usage, and generated invoices. Provide a button to trigger invoice generation.

Use shadcn/ui for components. Structure the project for Vercel deployment. Provide database schema, API endpoints with example requests, and frontend components. Prioritize clean architecture and testability.