QuickBooks Online error 9999 can be seen when a user tries to refresh the bank details in QuickBooks; we can fix the error by updating Financial Institution in QuickBooks Online by using the following steps:
- Open QuickBooks Online on your workstation.
- Move to the Banking tab.
- Under the Banking tab, click the Update option.
- Follow the same steps 2-3 times.
If the error persists, you need to talk to the QuickBooks support team by dialing the customer support number (855)-526-5749 to get assistance solving the QuickBooks Online Error 9999.