There are two common issues we see with new users of LedgerLink that result in a failure to connect to their QBO account.
1. Not using Master Administrator account
In order to authorize LedgerLink's connection to your QBO account, you must enter the credentials for a Master Administrator account in the connection dialog.
Otherwise you'll see this error from QBO.
2. Clicking Use Sandbox checkbox
A Sandbox is a demo QBO company loaded with sample data that is used by developers. Since you are trying to connect to your QBO account, you would not want this option checked.
If you leave the Use Sandbox option checked, you will see this error when you try to connect to your QBO account.