> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fynn.eu/llms.txt
> Use this file to discover all available pages before exploring further.

# Developers

> Integrate your application with Fynn via the API, webhooks, and advanced features

Fynn offers comprehensive developer tools to seamlessly integrate your applications with our platform. Whether you want to automate payment processes, synchronize customer data, or create custom workflows – you'll find all the necessary resources here.

## Quick Start

<CardGroup cols={2}>
  <Card title="API Reference" icon="book" href="/api-reference/introduction">
    Complete documentation of all API endpoints with examples.
  </Card>

  <Card title="Create API Key" icon="key" href="https://app.fynn.eu/settings/api-tokens">
    Generate API keys for authentication.
  </Card>
</CardGroup>

## Integration Options

### REST API

The Fynn API gives you complete access to all platform features. With the RESTful API you can:

* **Manage customers**: Create, update, and retrieve customer data
* **Control subscriptions**: Create, modify, and cancel subscriptions
* **Generate invoices**: Create, finalize, and send invoices
* **Process payments**: Add payment methods and manage transactions
* **Configure products**: Manage catalog with products and prices

<Card title="API Documentation" icon="book-open" href="/api-reference/introduction">
  Learn the API basics and explore all available endpoints.
</Card>

### Webhooks

Webhooks allow you to react to events in Fynn in real-time. You automatically receive notifications when:

* A new customer is created
* A payment is received or fails
* A subscription is started, changed, or cancelled
* An invoice is created or paid

<Card title="Set up Webhooks" icon="bell" href="/en/guide/webhooks/introduction">
  Configure webhooks for real-time events.
</Card>

### OAuth 2.0

For applications that access Fynn on behalf of users, we offer OAuth 2.0 authentication. This enables:

* Secure user authorization without password sharing
* Access to user-specific data
* Single Sign-On (SSO) integration
* OpenID Connect for identity management

<Card title="OAuth2 Flow" icon="lock" href="/en/guide/oauth2/introduction">
  Implement secure authentication with OAuth 2.0.
</Card>

### Fynn Functions

With Fynn Functions you can extend the platform logic and implement custom rules:

* **Checkout extensions**: Dynamic shipping costs, product options
* **Custom validation**: Own business logic in checkout
* **External API integrations**: Connection to third-party systems

<Card title="Fynn Functions" icon="function" href="/en/guide/functions/index">
  Extend Fynn with custom functions.
</Card>

## Authentication

All API requests require authentication via API key.

<Steps>
  <Step title="Create API key">
    Go to [Settings > API Keys](https://app.fynn.eu/settings/api-tokens) and create a new key.
  </Step>

  <Step title="Store key securely">
    The key is only displayed once. Store it securely.
  </Step>

  <Step title="Authenticate requests">
    Add the key as a Bearer token in the Authorization header:

    ```bash theme={null}
    curl -H "Authorization: Bearer YOUR_API_KEY" \
         https://coreapi.io/v1/customers
    ```
  </Step>
</Steps>

<Warning>
  Never share your API key publicly. Use environment variables to store keys securely.
</Warning>

## Development Environments

Fynn offers two environments for development:

| Environment    | API URL                      | Description                          |
| -------------- | ---------------------------- | ------------------------------------ |
| **Production** | `https://coreapi.io`         | Live environment for production data |
| **Preview**    | `https://preview.coreapi.io` | Test environment for development     |

<Tip>
  Use the Preview environment for testing and development before rolling out changes to production.
</Tip>

## Helpful Resources

<CardGroup cols={2}>
  <Card title="n8n Integration" icon="robot" href="/en/integrations/automation/n8n">
    Automate workflows with n8n and Fynn.
  </Card>

  <Card title="Postman Collection" icon="folder" href="/api-reference/introduction">
    Import the API into Postman for quick testing.
  </Card>
</CardGroup>

## Support

Need help with integration? Our developer support is available:

* **Email**: [hi@fynn.eu](mailto:hi@fynn.eu)
* **Book appointment**: [Schedule a consultation](https://cal.com/team/fynn/fynn-documentation)