Hi there, Allied3.

I can help you add the purchase order number in QuickBooks Online. 

You'll need to turn on the Use custom transaction numbers for expenses in the Account and Settings. This way, you can add the purchase order number in QuickBooks. 

Here's how:

1.  Go to the Gear icon at the top right to get to the Account and Settings. 

2. Select the Expenses menu at the left pane, then tick the Pencil (edit) icon in the Purchase orders section. 

3. Turn on the Custom transaction numbers option.

4. Hit Save and Done.

I've also added this article for more information about purchase orders: Create and send purchase orders in QuickBooks Online.

Keep your post coming if you have any other questions about adding purchase orders number in QBO. I'll be right here to help. Have a good one!