> 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/3d-secure/integrate-d1-api/d1-api-reference/outbound-api-from-d1.md).

# Outbound API (from D1)

Use outbound APIs when the **D1 backend** calls your **issuer backend**.

{% hint style="info" %}
Use the interactive reference pages below for day-to-day integration. Download the OpenAPI specs only if you want to import them into your tooling.
{% endhint %}

### Interactive API reference

* [OAuth 2.0 API](/3d-secure/integrate-d1-api/d1-api-reference/outbound-api-from-d1/oauth2-api.md)
* [Consumer API](/3d-secure/integrate-d1-api/d1-api-reference/outbound-api-from-d1/consumer-api.md)
* [3DS API](/3d-secure/integrate-d1-api/d1-api-reference/outbound-api-from-d1/3ds-api.md)

### Download OpenAPI specs

* [D1-Public-OUT-v1-Auth2.yaml](https://openapi.gitbook.com/o/fwy1mtbRONGA2YDKDBr0/spec/D1-Public-OUT-v1-Auth2.yaml) (OAuth 2.0)
* [D1-Public-OUT-v1-Consumer.yaml](https://openapi.gitbook.com/o/fwy1mtbRONGA2YDKDBr0/spec/D1-Public-OUT-v1-Consumer.yaml) (End Users)
* [D1-Public-OUT-v1-3DSecure.yaml](https://openapi.gitbook.com/o/fwy1mtbRONGA2YDKDBr0/spec/D1-Public-OUT-v1-3DSecure.yaml) (3DS)


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