Thank you for joining the conversation, EZ2. 

We can only print on QBO using Letter paper or those of that size range. You can find a third-party app that allows you to print receipts using thermal printers by clicking the Apps menu on the left-hand side.

I'd like to include this article in case you need it in the future: Fix QuickBooks Online printing issues on browsers for Windows.

You can always go back to this thread if you have any other questions in mind. Have a good one!