When is the Purchase Order number assigned?
As soon as a Purchase Order that you created is fully approved and sent to QuickBooks Online, its Purchase Order number is assigned automatically. These numbers ascend incrementally.
Please note: this is only the case if the "Custom No" option has been switched off in QuickBooks Online.
If this option has been activated, then QuickBooks Online does not assign any numbers to ApprovalMax Purchase Orders/Bills and the respective fields are left blank.