I want to get you pointed in the right direction to verify this iZettle connection, @katymedley.
QuickBooks integrates with various third-party applications. Thus, QuickBooks Online can be connected to iZettle.
However, to help determine if the account that you're using right now can be connected, I suggest reaching out to the iZettle support team. They'll be able to discuss with you the integration matter and provide the necessary actions that need to be taken.