Hi there,

Let me give you some information about PO Box in QuickBooks Online (QBO) Payroll. When setting up employees, QBO only allows addresses within the 50 states.

To ensure that your employees get to receive their tax paperwork, you have to make sure that the physical home address matches the IRS records. 

You may use this tool to verify if the address is within the allowed states in QBO: USPS Zip Code Database.

The website provides a searchable database where you may look for the zip codes of certain cities or street addresses.

To further assist you with your concern, I recommend consulting the IRS.

You may also want to read this article to learn more about how to pay or file state and federal payroll taxes online: Pay and file payroll taxes and forms in Online Payroll.
 

Let me know if you need further assistance with your addresses in QBO Payroll. I'm here to help anytime. Keep safe.