Http payload event

I have a question as a beginner:
i use c# and webapi. i have set up a post endpoint. I want chirpstack to send data to it. This also works, the controller is called.

[HttpPost]
public IActionResult ReceiveData([FromBody] object data)
{

return Ok();

}

It is called because I used the general “object” as data type. But I want something like MySensorData.

[HttpPost]
public IActionResult ReceiveData([FromBody] MySensorDatadata)
{

return Ok();

}

As I understand it, all data of the event is sent. This means that I have to recreate such an event type so that the data lands there automatically. But where can I find the complete definition of such an event?

Thanks for your help!