I am unable to invoice a billable labor hour to show up in Finance > Billing review > Labor hours.
This occurs if the time entries weren't approved. To allow invoicing of non-approved or submitted time entries so that they can still be invoiced. You will have to make changes in company settings. If this not feasible, you will have to ensure that the employee's timesheet is submitted and approved to be seen in the billing review.
Admin > My Company > Company Settings > Invoice > Post T&M entries - All
Please contact Kaseya Support if you continue to receive this error.