negative invoice

[Lewis Overton]

A vendor overcharged for services. They have now sent a new invoice with a
new charge (legitimate) and a credit for the overcharge. The total is
negative and gnucash says I can't post an invoice with a negative credit.
The overcharge was in the previous fiscal year.

How can I enter the invoice with the correction so that my accounts payable
correctly reflects the transaction?

I'm using gnucash 2.2.1 installed via Fink on a MacBook Intel.

Lewy