It will have a *path operation* that will receive an `Invoice` body, and a query parameter `callback_url` that will contain the URL for the callback.

This part is pretty normal, most of the code is probably already familiar to you:

```Python hl_lines="9-13  36-53"
{!../../../docs_src/openapi_callbacks/tutorial001.py!}
```

!!! tip

* The alternative documentation will also reflect the new query parameter and body:

![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)

### Recap

In summary, you declare **once** the types of parameters, body, etc. as function parameters.

You do that with standard modern Python types.

        for ((parameter, type) in typeArguments) {
            val ktParameter = typeParameters.getOrNull(parameter.index) ?: return emptyMap()

            // i.e. we were not able to infer some types
            if (type.contains { it: UnwrappedType -> it.constructor is TypeVariableTypeConstructor }) return emptyMap()

            result[ktParameter] = type.toKtType(analysisContext)
        }

* The alternative documentation will also reflect the new query parameter and body:

![ReDoc](https://fastapi.tiangolo.com/img/index/index-06-redoc-02.png)

### Recap

In summary, you declare **once** the types of parameters, body, etc. as function parameters.

You do that with standard modern Python types.

    * Add new `root_path` parameter for `FastAPI` applications to provide it in cases where it can be set with the command line (e.g. for Uvicorn and Hypercorn, with the parameter `--root-path`).
    * Deprecate `openapi_prefix` parameter in favor of the new `root_path` parameter.

* Klicken Sie auf die Taste „Try it out“, damit können Sie die Parameter ausfüllen und direkt mit der API interagieren:

![Swagger UI Interaktion](https://fastapi.tiangolo.com/img/index/index-04-swagger-03.png)

* Klicken Sie dann auf die Taste „Execute“, die Benutzeroberfläche wird mit Ihrer API kommunizieren, sendet die Parameter, holt die Ergebnisse und zeigt sie auf dem Bildschirm an:

* Ambos _paths_ toman operaciones `GET` (también conocido como HTTP _methods_).
* El _path_ `/items/{item_id}` tiene un _path parameter_ `item_id` que debería ser un `int`.
* El _path_ `/items/{item_id}` tiene un `str` _query parameter_ `q` opcional.

### Documentación interactiva de APIs

    <module>maven-model</module>
    <module>maven-monitor</module>
    <module>maven-plugin-api</module>
    <module>maven-plugin-descriptor</module>
    <module>maven-plugin-parameter-documenter</module>
    <module>maven-plugin-registry</module>
    <module>maven-plugin-tools</module>
    <module>maven-profile</module>
    <module>maven-project</module>
    <module>maven-reporting</module>

</div>

Open your browser at <a href="http://127.0.0.1:8000" class="external-link" target="_blank">http://127.0.0.1:8000</a>.

There you can set:

* The "Item ID", used in the path.
* The "Token" used as a query parameter.

!!! tip
    Notice that the query `token` will be handled by a dependency.

With that you can connect the WebSocket and then send and receive messages:

<img src="/img/tutorial/websockets/image05.png">

}
```

### Setting the `root_path` in the FastAPI app

Alternatively, if you don't have a way to provide a command line option like `--root-path` or equivalent, you can set the `root_path` parameter when creating your FastAPI app:

```Python hl_lines="3"
{!../../../docs_src/behind_a_proxy/tutorial002.py!}
```