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

# The Prefer HTTP header

> Forcing desired responses from the Bango Payment Merchant API

To help you test your store, in many cases you can specify in a Bango Payment API request the kind of response you want. For example, when sending an initial request to identify a user, you can force an `OK` response that returns a Bango ID straight away. You can use this mechanism to trigger testing scenarios that you don't usually encounter naturally or can't simulate, such as failures by payment providers.

To force certain responses, include one or two special HTTP headers in the API request:

* `Prefer`: specifies which HTTP status code to respond with
* `preference-extension`: specifies values you need in the response body, to disambiguate responses with the same HTTP status code

Check [Bango Payment / Merchant API reference](/legacy/dcb-payments-v5/api-reference/index) to see whether you can use a `Prefer` header to force a particular response. If you can't, you may alternatively be able to use [Bango TestPay](/legacy/dcb-payments-v5/testing/bango-testpay) to force that response.

Never include a `Prefer` or `preference-extension` header in production.

### `Prefer` header

| Syntax | `Prefer: status=NNN` |
| - | - |
| Examples | `Prefer: status=200 Prefer: status=404` |

Use this header with a Bango Payment API request to force a response with the specified HTTP status code. For example, if you specify `Prefer: status=401` with an API request you'll always receive an HTTP 401 response, and the response body will specify `responseCode` as `UNAUTHORIZED` to match the appropriate [API definition](/legacy/dcb-payments-v5/payment-provider-api-reference/index).

Some HTTP status codes correspond to more than one `responseCode` in the response body. For example, HTTP status 202 might mean a `responseCode` of `USER_CANCELLED` or `NOT_AVAILABLE` or others, depending on the API in use. To choose which `responseCode` to receive, include the `preference-extension` header.

### `preference-extension` header

| Syntax | `preference-extension: responseCode=XXX[;action=YYY]` |
| - | - |
| Examples | `preference-extension: responseCode=CLIENT_ACTION_REQUIRED;action=REDIRECT preference-extension: responseCode=USER_CANCELLED preference-extension: responseCode=PRICE_NOT_SUPPORTED` |

Use this header **together with** `Prefer` to select the response you want if the HTTP status code matches multiple possible responses. See [Bango Payment / Merchant API reference](/legacy/dcb-payments-v5/api-reference/index) for details of status codes and how they relate to `responseCode` values.

### Examples

Force `UNAUTHORIZED`:

| Request headers | `Prefer: status=401` |
| - | - |
| Example response | `{ "responseCode": "UNAUTHORIZED", "responseMessage": "Invalid access credentials." }` |

Force `CLIENT_ACTION_REQUIRED` with action `REDIRECT` (for those API calls supporting this response):

| Request headers | `Prefer: status=202 preference-extension: responseCode=CLIENT_ACTION_REQUIRED;action=REDIRECT` |
| - | - |
| Example response | `{ "responseCode": "CLIENT_ACTION_REQUIRED", "responseMessage": "An action is required in the client.", "sessionId": "9c7b9891-c871-4dd5-bdcc-ac25ff2412b7", "bangoUserId": null, "parameters": { "action": "REDIRECT", "url": "http://www.example.com/id/parameter=6bd6305c" } }` |

Force `DECLINED` (for those API calls supporting this response):

| Request headers | `Prefer: status=202 preference-extension: responseCode=DECLINED` |
| - | - |
| Example response | `{ "responseCode": "DECLINED", "responseMessage": "The payments provider declined the payment request." }` |