Thank you for getting back, @james-braund.
Allow me to share additional insights towards the connection between your app and QuickBooks.
There's no integration available yet between your app and QuickBooks. Thus, you need to set up iZettle as a bank account in the program, then manually record your iZettle sales.
Once done, you're now ready to create your transactions from the (+) New menu, or import an Excel CSV file as suggested by JenoP above.
For additional references, while working with banking and reconciliation, you can open this article.
Let me know if you have any other questions by adding a comment below. I'm more than happy to help. Have a good day!