Do you have the QuickBooks Online App installed on your Mac? If so, let's try to troubleshoot this issue by clearing the app's cache. This is how we can restore the connection.
- Quite QuickBooks Online for Mac App.
- Hold down the Fn (function) key and open it again.
- It will ask if you want to reset the app. Click the Reset button.
- Open the app again.
Please refer to this article for details: QuickBooks App for Windows and Mac: General support.
Let us know if you have any questions. Thanks!