Create dataset in direct query mode using the PowerBI Rest API

Hello everyone!
from the documentation of the PowerBI REST API, I suppose that the correct API to be invoked in order to create a dataset is "Push Datasets - Datasets PostDatasetInGroup" (https://docs.microsoft.com/en-us/rest/api/power-bi/pushdatasets/datasets_postdatasetingroup).
Anyway I cannot understand what are the correct parameters to send in post (in addition to the authentication token clearly ..)
There are only one example but isn't esaustive for me.

Where is the Direct Query mode declaration?
Where is the declaration of type of datasource set? (for example ... Azure SQL, Spark HDInsight, etc.)
The connection credentials?

Is it possible to see some complete example of creating datasets in direct query mode?

Thank you so much for the support !!

Regards,

   Alfredo