If you have 2 or more invoices that relate to 1 purchase order the below steps walk you through splitting the order into several orders.
Locate order.
Click into the Invoice Tab, and Confirm Invoice.
Scroll down, and click create Split Order.
This order will be given a new order ID number with the letter SP at the end indicating this is a split order.
You will be taken to the purchase order tab to enter the Quantities (QTY) of the products you require on the secondary invoice.
Click Save & Complete to complete.