Quickbooks online Error 9999 is a common occurrence when using QuickBooks. The bank website cannot be accessed by QuickBooks Online due to error 9999. In the event of an error, a system may hang, respond slowly, or simply cease to work. These effects can be severe.
If you attempt to update your bank details in QuickBooks, QuickBooks will display a banking error. QuickBooks Online Support can assist you if this occurs.