First of all, yes, I know that IIF (Intuit Interchange Format) files are a deprecated way of transferring data into Quickbooks Desktop.
However, I have been tasked with writing a PHP script that will create an IIF file that a customer could use to import an invoice that is created by my web application. If it were my choice, I wouldn't attempt to use IIF.
The Question:
Using an IIF import, is it possible to have Quickbooks use either its internal ids, an account number (which ends up in the NOTE field), or a custom field to link the customer to the invoice rather than using the NAME field?
It appears the answer is no.
The closest thing I could find to an answer was from here: https://community.intuit.com/questions/1575622-how-do-you-import-iif-file-using-a-custom-field-as-identifier
The answer from that link:
"Custom Fields are not a Key Field; Vendor Name is the Key Field. You cannot import Bills except by reference to the Relational key field of Vendor Name. This is a relational database, so the things that matter are the Key Fields. AP and Vendor Name, at a minimum, define Bills."
My question was about transactions rather than Bills, but I imagine that the same answer that applies to Bills applies to Invoices and the customer Name.