There is no barcode scanning in QuickBooks Online. This is only available using QuickBooks Point of Sales   and QuickBooks Enterprise inventory solution.   If you are in need of a scanner, seems like you are in a retail sales environment.  Even if you get this to work, the latency will turn into an issue.  Inventory adjustment will only be available in QBO Advance which subscription tag by the time of the end of a year, you will had paid in full a perpetual POS license with the full retail store capabilities.

There are a number of virtual POS out there that sales you the scanner, but will offer no financial accounting.  Only QB POS is fully interactable with your QB financial. The new version of QB POS has great features that sync with your E-Commerce website. 

Hope this help.