Solution
To resolve this error, follow these steps:
Log into LeanLaw and navigate to Settings by clicking the gear icon in the top right corner.
Scroll down to Integrations and select QuickBooks.
Click Edit Expense Settings.
Ensure that the Enable QuickBooks Sync option is turned on.
Locate the Default QuickBooks Services field and select an appropriate service.
If no service appears, check QuickBooks to confirm that a corresponding service exists or create one.
Save changes and retry setting up the expense sync.
Once these steps are completed, LeanLaw should be able to sync expenses with QuickBooks without displaying the error.
For more details, please refer to this article on how to properly set up expense sync with QuickBooks Online: Set Up Expense Sync with QuickBooks Online.