Indeed, the default request type of the data source is GET. Please note that you will need to allow returning JSON result on GET requests:
To be sure that this is the cause of the problem use the browser's developer tool to verify what the response from the server is and check for any errors.
As to the filter parameters, the data source sends a list of filters to the server. You can get them from the QueryString.
You can also check this project
, which shows how to use Dynamic Linq to parse the filter parameters and use them to filter data.
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