In new QBO, they’ve up to three custom fields selections available to customize invoice layout.
You can pick one field for Client Purchase Order Number.
From the Home page screen
- Select the Company Gear (located top upper corner)
- Select “Company Settings” under Settings header
- Select “Sales” under Settings”
- Select “Sales Form Content”
- Select “Custom Fields”
- This is where you add Client PO No.
- Save and Done
- See screenshot photo below for reference