# Getting started

This reference is key for your comprehensive understanding of Hellgate and, as such, essential for the successful use of our payment orchestration products.

Hellgate APIs make use of RESTful conventions when possible and where it makes sense. All calls use the standard HTTP verbs to express access semantics, like `GET`, `POST`, `PATCH`, and `DELETE`. Other related conventions for our API can be found in the section below.

Gated Features
Some of the features offered by Hellgate are gated and require explicit activation. These features are clearly labeled with a `Gated` badge.

In order to get access you need to contact your account manager.

Beta Features
Hellgate offers various features as part of our beta release track. These features are clearly labeled with a Beta badge in the documentation and interface.

By default, accounts do not have access to beta features unless explicitly subscribed to beta releases. If you would like to enable beta features, please
contact your account manager for subscription options.

**⚠️ Beta features are experimental and subject to change or removal at any time. They may also have limited support and stability.**

## JSON Conventions

- Resources are addressable by a UUIDv4 `id` property.
- Property names are always in `snake_case`.
- Hellgate does not support empty strings. To unset a string value, use an explicit `null` value instead.
- Temporal data is encoded in [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) strings.


## Authentication

Hellgate supports API keys to authenticate requests.

The keys are passed in via the HTTP header `x-api-key`.


```bash
curl --header 'X-API-Key: <SECRET>' \
  --request POST 'https://api.hellgate.io/...'
```

The keys must be handled with care and kept secure. Never hardcode the API keys in your source code, but keep them solely on your backend systems.

## API Use

### API Versions

Hellgate API will be updated regularly, to include new features and updates to existing ones. We package these changes into versions that can be addressed using a header field (`x-hellgate-version`).

If the there is no version specified in the header, the most recent version is being used.


```bash
curl --header 'x-hellgate-version: <SELECTED VERSION>' \
  --request POST 'https://api.hellgate.io/...'
```

Hellgate sets the `x-hellgate-version` header on API responses, to tell the integrator which version is in use.

### Idempotency

To prevent your system from handling requests twice and thus, for example, charging a customer twice, Hellgate supports idempotency on requests to the API.

The behavior is controlled via the header field `x-idempotency-Key`.


```bash
curl --header 'x-idempotency-key: <key>' ...
```

### Pagination

Endpoints that return lists of objects support cursor-based pagination requests. By default, Hellgate returns up to 50 objects per API call. If the number of objects in a response from a support endpoint exceeds the default, then an integration can use pagination to request a specific set of the results and/or to limit the number of returned objects.

If an endpoint supports pagination, the response body follows this structure:


```json
{
  "current_page": 1,
  "page_size": 50,
  "total_items": 200,
  "total_pages": 4,
  "data": [...]
}
```

The single pages can be requested with query parameters:

| Parameter | Type | Description |
|  --- | --- | --- |
| `limit` | `integer` | The maximum amount of objects to be returned on a page. |
| `page` | `integer` | The requested number of the page to return. |


### Request Errors

Hellgate uses the standard errors to indicate the client errors on the gateway level.

Invalid Requests - HTTP 4xx
The response payload for processing errors follows a standard format.


```json
{
  "status": "the HTTP status code",
  "classifier": "the classifer of the error",
  "message": "interesting for humans..."
}
```

Unprocessable Content - HTTP 422
The response payload for processing errors follows a standard
format which includes the validation errros.


```json
{
  "status": "the HTTP status code",
  "classifier": "the classifer of the error",
  "message": "interesting for humans...",
  "validation_errors": [
    {
      "path": "a JSON path pointing to the wrong data",
      "message": "something interesting for humans..."
    }
  ]
}
```

### Business Errors

The processing errors refer to the primary functions of Hellgate and not necessarily to the related business logic. For example, a failed authorization due to insufficient funds will result in a 200 response, as the payment layer could successfully process the request (even though the business result is negative).