I am changing an employee monthly to biweekly. I have already paid him up to 12/1/23. When I change it to twice a month, it shows the pay pay period as 12/2 to 12/12

Hello there, JP. Let's work together to adjust the pay schedule to bi-weekly in QuickBooks Online (QBO). 

When changing the pay schedule for your employees, let's make sure to choose the correct next payday and the end of the next pay period to match the new pay schedule.

Here's how:

1. Go to the Payroll menu in the left panel.
2. Select the Employees tab.
3. Select the employee you want to change the pay schedule.
4. Go to Employment Details then click the pencil icon.
5. Change the pay schedule and click Save when done.
    

Additionally, I've included this resource that will help you track where you're business stands in terms of payroll and employee expenses: Run payroll reports.

Also, you can check out this link if in case you want to create an unscheduled check for the current pay period in the future.

Keep your posts coming if you need further assistance with changing employees' pay periods in QBO. I'll be standing by for your response. Have a great day and stay safe.