Thanks for reaching out to us about this, rgonzalez1.
The Error 9999 is a script error that interrupts the connection of your bank and QuickBooks Online (QBO). This error can be resolved by logging into your bank website to check if there are notifications and/or alerts that need your attention. Then, try to manually updating your bank account to refresh the connection.
Go to the Banking tab.
Select the bank account and click Update.
If prompted, enter your Multi-Factor Authentication (MFA) credentials and select Continue update.
Also, may I know the what is your financial institution? These details would help me review our system for any related issues.
You can always go back to this thread if you have other questions. It's my pleasure to help in any way I can. Have a good one.