Receiving an empty body in retrofit Response

Please check your JsonObject. If you want to get response in json you must be define a response type JsonObject not JSONObject other wise specify the pojo class in your interface.

you should try like this way ....

public interface SlotsAPI {

/*Retrofit get annotation with our URL
  And our method that will return a Json Object
*/
@GET(url)
Call<JsonElement> getSlots();
}

in request method

 retrofit.Call<JsonElement> callback = api.getSlots();
callback.enqueue(new Callback<JsonElement>() {
@Override
public void onResponse(Response<JsonElement> response) {
    if (response != null) {
        Log.d("OnResponse", response.body().toString());
    }
}