The integration between iZettle and QuickBooks Online is unavailable, user63666.
This might be the possible reason you're getting the error message. Therefore, I suggest setting up iZettle as a bank account, then manually record your sales in QuickBooks.
Here's how:
- Go to the Accounting menu.
- On the Chart of Accounts tab, select New.
- Choose the Account and Detail types and then make iZettle as the name.
- Click Save and Close.
Once done, you can now create your transactions from the + New menu, or import an Excel CSV file in QuickBooks Online.
Additionally, it's a best practice to reconcile your account monthly to ensure it matches your iZettle statement. To learn more about this process, I encourage visiting this article: Reconciling An Account.
If you have follow-up concerns about this or should you need anything else, please let us know. Doing so helps us to further assist you.