Unable to retrive purchase order and lines using the dispatch object mentioned on the description

using (DispatchObject poObject = new DispatchObject(pvx.InvokeMethod("NewObject", "PO_PurchaseOrder_bus", oSS.GetObject())))

Could any one of you suggest, which dll or nuget to be used for this dispatch object.

We are using the below object management, but it retrieves zero records.