There appear to be some issues with payroll updates and other critical updates related to QB2019. My experience was a continual "A critical update...close and reopen" and then this week failure of payroll update. It took repairing the installation of QB2019 to fix it. I would have your client attempt to repair at their end keeping in mind they need to shut off multi-user and have everyone but master admin logged off to repair.
Have them follow the steps here h and you may need to do the same on yoru install ttps://quickbooks.intuit.com/community/Help-Articles/Fix-error-when-updating-Desktop-or-Payroll/td-p/228505 and then turn multi-user back on and try again