As an example :
on posman/curl the following call is returning some entities :
GET: https://api.smartsheet.com/2.0/folders/9999/children
The c# wrapper call such as :
SmartsheetClient.FolderResources.GetFolderChildren(9999, null, null, null, null, null, null);
On postman the fileds createdAt and modifiedAt have values for the sheets but not on the c# wrapper.