> For the complete documentation index, see [llms.txt](https://docs.payments.thalescloud.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.payments.thalescloud.io/xpay-enablement/api-reference/guidelines.md).

# Guidelines

## Development Considerations

The following changes are considered backwards compatible:

* Adding a new API request
* Adding new optional parameter to existing API (request/response)
  * This parameter could be added as body, HTTP parameter or HTTP header
* Adding new value on enum
* Making mandatory parameters optional
* Ignore any unknown fields/values received as part of API request/response

## Correlation of APIs

All API calls related to the same use case shall use the same **x-request-id (TSP API v1) or x-correlation-id (TSP API v2)** value.

*Note for TSPs implementing also the* [***Issuer Gateway API***](https://tsh-issuer-gateway.docs.stoplight.io/)*:*\
*The value provided in the **x-correlation-id** HTTP header is maintained across all API calls for digitization flow.*\
*The same applies for lifecycle flows.*


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