I'll be happy to explain how to show a product was sold in QuickBooks Online.
In order to do this, you'll need to turn on inventory tracking. To complete this, follow these steps:
Select the Gear icon on the Toolbar.
Under Your Company, choose Account and Settings (or Company Settings).
In the left sidebar, select Sales.
Select the pencil next to Products and services and mark the option Track inventory quantity on hand. (Note: This will enable the new item type called Inventory item when selecting New under Products and Services.)
For more information on Inventory tracking, click here.
If you have any trouble setting this up, please let me know below. I'll be keeping an eye out for your reply.