Sheldon Boone said:

Is there a preference and or setting in Sage to have an auto invoice number created when you make payment to a vendor PO?

No.  You autonumber the PO as you indicated, but the vendor numbers the invoice based on their policies and gives it to you on the invoice.  However, you need the PO converted to an invoice before making the payment if you already created it and didn't pay anything when you created the PO entering it as Pay Later.

Your payment numbering is determined by you method of payment.  If it is by cheques, you may be looking for Setup, Reports & Forms, Cheques, pick your bank account, Cheque Settings.  But you are paying the invoice at this point, not the PO.

Sheldon Boone said:

If so, can you turn it off?

Turning off autonumbering is as simple as deleting the number currently in the setup area.