On a PO invoice usually the only reference you have is a PO number, and you do not have any detailed information which is currently needed with import of PO vendor invoice lines. This results in that you have to provide the most pertinent information with data provided from operations in order to import the invoice using Vendor Invoice Automation.

There should be support for wholesale defaulting of PO lines to invoice lines or product receipt, in this way there could be minimal invoice information and you do not need to access Operations data in order to do the import of the invoice.

In addition there should also be a function where you can create a purchase order from the imported pending invoice, and also a form for vendor invoice lines that failed to import (similar to existing 'Vendor invoices that failed to import')

Ref:

https://docs.microsoft.com/en-us/dynamics365/unified-operations/financials/accounts-payable/vendor-invoice-automation