Proper place for "Request" classes

[BohdanTron]

In the solution, CustomerOrderRequest and RegisterCustomerRequest classes are responsible for receiving data from the outside and passing it to the Application level. However, CustomerOrderRequest is placed at the API level, while RegisterCustomerRequest is at the Application level. So, what is the best place for such classes, and why is it better not to use Commands directly as input API parameters?

Thanks in advance