The integration between QuickBooks Online and Square has its own limitation at the moment, vaneprovin.

It's currently a one-way integration which we only receive data from Square. This means you'll need to update the quantity of the product in Square first. QBO will then mirror the information once we receive daily updates from them. 

We'll send your feedback directly to our engineers. Updates and product enhancements are often based from feedback and suggestions that are sent to them.

The Community is always ready to help you again if you have other questions.