Hello, RobinM21.
Let me share some information why you're unable to connect your square multiple location in QBO.
QuickBooks integration doesn’t support Square’s Multiple Location feature. Only one Square account can connect with QuickBooks Online at one time.
You need an third party app as what Fiat Lux - ASIA suggested. You can visit the Intuit App store to find one that best suits your business.
Please know that I'm just a post away if you have any other QuickBooks concerns. I'll be delighted to be your guide once more. Have a great day ahead.