> For the complete documentation index, see [llms.txt](https://amast-einvoice.gitbook.io/amast-einvoice-sass/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://amast-einvoice.gitbook.io/amast-einvoice-sass/authentication.md).

# Authentication

Every API request must include your **API key**. The key resolves your **tenant** (organisation) and environment. There is no separate secret header.

## Accepted headers

Use **one** of:

```
Authorization: Bearer YOUR_API_KEY
```

```
X-API-Key: YOUR_API_KEY
```

## JSON requests

For endpoints with a body:

```
Content-Type: application/json
```

## Errors

| HTTP  | Meaning                    |
| ----- | -------------------------- |
| `401` | Missing or invalid API key |

Example:

```json
{ "message": "API key required (Authorization: Bearer or X-API-Key)" }
```

## Security

* Call the API **only from your backend** (or trusted server).
* Do **not** embed keys in frontends, mobile apps, or public repos.
* Rotate keys from **API Keys** if a key may have leaked; update integrations before revoking the old key.
* Use separate keys per environment (sandbox vs production) where possible.


---

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