For companies integrated with QuickBooks Online and Xero, there is the option to match and fulfill Purchase Orders when posting through invoices from AutoEntry.
In the single invoice view, simply click on the Sync icon to the right of the PO field:
This will pull through a list of all open POs for that supplier and populate the drop-down menu. Simply click on the drop-down to select the relevant PO you want to apply the invoice to. If the PO selected does not match the amount on the invoice a notification will also pop up to alert you. The invoice will still process through and part-fulfill the PO.
For Xero integrations there is also a button to open the purchase order in Xero in a separate tab: