### Key Concepts
* **Authentication:** Every request to the API must be authenticated using a
secure key pair. See the **Authentication** section below for details.
* **Rate Limiting:** All API calls are subject to rate limits to ensure fair
usage and stability. See the **Rate Limiting** section for a full
explanation.
* **IP Restrictions:** For enhanced security, you can optionally restrict
your API keys to a specific set of IP addresses from within your Trading 212
account settings.
* **Selling Orders:** To execute a sell order, you must provide a
**negative** value for the `quantity` parameter (e.g., `-10.5`). This is a
core convention of the API.



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