We are currently in the process of improving our QuickBooks Online integration and have disabled the link on the sync page for new QBO integration users. The link will be enabled when we release our new QBO sync product. Please check back in several weeks.
Existing QBO sync users may continue to use the sync product during this transition. However, if a current user disables QBO sync, the user will not be able to re-enable until the new product is released.