Usind AddItem method of RCOIS (Remote Complex Object Instance Service)

Hi All,

My requirement is to add a new Product/Package under the Root Product (Root Line Item) during the New Registration order process being invoked by an interface. I am currently using AddItem method of RCOIS with the below inputs

but the Item is not getting added under the Root Line Item. Only if I use SyncInstance after add item does the new line item is being added. But if i need to add another item/ product then again if the syncinstance is called the old add on gets removed and new one gets added. Could you please help if without synchinstance, additem works or not. Please find the attached xml of the test workflow I created.