This functionality works with Sage Line 50 & may work on other Finance packages.

In an unusual circumstance, you can have line 1 on a credit note, with zero value, followed by other lines with credit note values. When you upload that transfer file into your Finance package, then that credit note peculiarly becomes an invoice! That behaviour arises when your 1^st Traffic LIVE Invoice line item is zero value – That determines the transaction type for all lines with that reference number. Now don’t be alarmed as this is very unusual series of events. It's fixable !

If it does happen, what you can do is, Edit the “Invoice” in Sage Line 50, after loading the sales invoice with Import Plus, but before you update the Ledgers. In Sage Line 50, you change Type = “Invoice” to Type = “Credit Note” Save Close.