passing values to method

Question

I have ,
public void AddAsync<T>(T entity) where T : IEntity; method from DataService class

I have class SalesReceipt
and i want to add this SalesReceipt in AddAsync method .
like
DataService dataService = new DataService(serviceContext);

                   OnlineSalesReceiptQBEntry SalesReceipt = new OnlineSalesReceiptQBEntry();
                   SalesReceipt .AutoDocNumber = "1010";
                   SalesReceipt .ApplyTaxAfterDiscount = "True";
                   dataService.AddAsync(SalesReceipt );//error line

How to call this method/ add SalesReceipt to AddAsync().