Hi Sanjay,
You just need Workflow ID of the Shopping cart to use SWIA. However if you are looking specifically to forward work item as Admin forward via SWIA you need to get the workitem ID from Workflow ID. There are various way to get that one of the easiest way is to execute SWI5 and enter US and approver's user ID and select "Work items to be completed" in drop down.
Get the shopping cart workitem ID from there and then via SWIA forward it.
Thank you
Ritesh