What triggers the invoice print for installment invoices?

Apparently, my AR users have been having a problem with invoice printing that has been going on for years:

Currently when we setup payment terms for customers that include more than one installment, all of the installments print together when the order invoices.

 

When we setup the payment terms, we set them up to print 30 days prior to due date but that's not happening.

 

Please find out how we can have Oracle print each installment 30 days before due date.

They generally set up a new payment term for each order. These seem to be done correctly. They put the payment term on the sales order and interface the SO to receivables. The term id on the AR transaction matches the payment term id in OE nearly 99% of the time, so that is working.