To create the callback *path operation* use the same `APIRouter` you created above.

It should look just like a normal FastAPI *path operation*:

* It should probably have a declaration of the body it should receive, e.g. `body: InvoiceEvent`.
* And it could also have a declaration of the response it should return, e.g. `response_model=InvoiceEventReceived`.

```Python hl_lines="16-18  21-22  28-32"

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

## Example upgrade

Now modify the file `main.py` to receive a body from a `PUT` request.

Declare the body using standard Python types, thanks to Pydantic.

```Python hl_lines="4  9-12  25-27"
from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

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

## Example upgrade

Now modify the file `main.py` to receive a body from a `PUT` request.

Declare the body using standard Python types, thanks to Pydantic.

```Python hl_lines="4  9-12  25-27"
from typing import Union

from fastapi import FastAPI
from pydantic import BaseModel

This is normally called a **webhook**.

## Webhooks steps

The process normally is that **you define** in your code what is the message that you will send, the **body of the request**.

You also define in some way at which **moments** your app will send those requests or events.

* Automatic data model documentation with <a href="https://json-schema.org/" class="external-link" target="_blank"><strong>JSON Schema</strong></a> (as OpenAPI itself is based on JSON Schema).

* 🌐 Add German translation for `docs/de/docs/tutorial/body-fields.md`. PR [#10310](https://github.com/tiangolo/fastapi/pull/10310) by [@nilslindemann](https://github.com/nilslindemann).
* 🌐 Add German translation for `docs/de/docs/tutorial/body.md`. PR [#10295](https://github.com/tiangolo/fastapi/pull/10295) by [@nilslindemann](https://github.com/nilslindemann).