QuickBooks Error 9999 is a common online banking error that disrupts the connection between QuickBooks Online and a user’s bank account. When users encounter this error, they typically see a message stating that the program is unable to update their banking information. The error occurs due to several factors that interrupt the synchronization between the banking system and QuickBooks Online. Here’s an in-depth exploration of the main causes behind QuickBooks Error 9999, the signs of the error, and potential solutions for resolving it.