If your subscription package with QuickBooks Online gives you class tracking as a feature, you can use that functionality in Receipt Bank to assign location, client, and project classes to expense items.
Your class tracking codes will be available to you under the Class and Customer (client) fields in Receipt Bank.
You'll notice these two fields will be present in both your supplier entries in the 'Suppliers' tab and the individual 'Item Edit Pages' in your Inbox.
To maintain your Classes, click on the left-hand menu and into the Classes Tab. Then click the green Reload List button to update the list with the latest classes from your QuickBooks Online integration.