It’s a script error that QuickBooks has to fix. You will need to report it to them.
Resolution for 'accounts update issue: 'I keep getting code 9999. Why won’t my accounts update?' available: Yes.
The accounts update issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the accounts update issue yourself by looking for a resolution described in the article. If it is a complex accounts update issue or you are unable to solve the issue, you may contact us by clicking here or by using other accounts update support options.
For more information about resolving issues related to accounts update in Quickbooks/QBO or to get support for the issue 'I keep getting code 9999. Why won’t my accounts update?', click the link below: