How do you add a purchase order number to a invoice ?

Hello, alldowns20. I'm here to walk you through adding a purchase order number to an invoice. 

There are 2 ways on how to accomplish this. We can:

• add a custom field and enter the purchase order number manually.
• enter the purchase order number manually in the DESCRIPTION column.

Here's how: 

1. Go to the Gear icon at the top and then, select on Custom Form Styles.
2. Press on New Style and then choose Invoice.
3. Click on Content.
4. Hit on Custom Field at the bottom.
5. Put a check mark the box and label it.
6. Tick on Done to save it.

We may assign the also PO numbers on the Description field of the sales transaction. See this:

We can read this article for more details: Add custom fields to sales forms and purchase orders in QuickBooks Online.

Also, you may want to check out this article as your reference to guide you in personalising and adding specific info to your sales forms in QBO: Customise invoices, quotes, and sales receipts in QuickBooks Online.

Let me know if you have other concerns about customising sales forms and managing purchase orders in QBO. I'll gladly help.