Best answer by PaulKortman
When a new invoice is created in QB you'd need to record the QB Doc ID in the second system you're using to track these invoices, say a spreadsheet or airtable or something like that.
Then when QB notifies (via webhook) your zap that an invoice with QB Doc ID of x was updated you could query the spreadsheet/airtable for that QB Doc ID and get the invoice number, from there you could use the native Quickbooks Integration to "Find Invoice" using that invoice number and viola you have the invoice details to then update the spreadsheet/airtable information with.
This wouldn't work for creating, but it would work if all you need was to have updates to invoices. As long as your database (spreadsheet/airtable) had all of the invoice and QB Doc ID's in it, you'd be golden.