Allow negative amount in invoice

How is it possible to create an incomming invoice (expenses/bills) with a negative amount?

A supplier made a mistake in one invoice and to correct that payment he send a second invoice with a negative amount. But it's not possible to enter negative values into the amount field.

Since it is kind of incomes/revenues I tried that as well but there I am only able to select a customer, not a vendor.

<p>How is it possible to create an incomming invoice (expenses/bills) with a negative amount?<br /><br /></p><br /> <p>A supplier made a mistake in one invoice and to correct that payment he send a second invoice with a negative amount. But it's not possible to enter negative values into the amount field.</p><br /> <p>Since it is kind of incomes/revenues I tried that as well but there I am only able to select a customer, not a vendor.</p>

Hello? Is anybody here in this forum?

<p>Hello? Is anybody here in this forum?</p>