Let's make sure you can import purchase order (PO) numbers to invoices, tglockler.

Purchase numbers are unique identifying numbers. These are documents detailing the buyer's intention to purchase goods or services from a specific vendor or supplier. 

Thus invoices include the purchase order number so the invoice details can be compared and checked for discrepancies when an invoice and PO matching occurs as part of the verification of a vendor invoice process before payments. 

For now, you'll have to search for a third-party application online that can help you with the process. While the option isn't yet available, you can manually enter the PO number in your invoices.  To do so, you'll want to set up a custom field for the number. I've outlined the steps below:

1. Go to the Gear ⚙ icon and select Custom fields.
2. Choose Add field. If this is your first time creating a custom field, pick Add custom field.
3. Enter a name in the Name field.
4. Tick the All Sales forms or Purchase Order checkbox. Or, select both.
5. (Optional) To show the custom field on printed and delivered forms, turn on Print on form. Otherwise, it’ll only appear in QuickBooks Online.
   
6. Hit Save.

Moreover, customers can pay using a credit card, or ACH bank transfer by following the link in the email. To give you more details, I've added this article for reference: Take And Process Payments In QuickBooks Online With Quickbooks Payments.

Fill me in if you have any questions about sales. The Community is always right here to help you all the time.