If the seller has undercharged the buyer, he sends him a debit note for the amount of the undercharge. A debit note is in the nature of a supplementary invoice. If he has overcharged the buyer, the seller sends him a credit note. Credit notes are also issued to buyers when they return either goods (as where the are unsuitable) or packing materials on which there is a rebate. Credit notes are usually printed in red to distinguish them from invoices and debit notes.
Sample seller sends debit note
22nd August 2010
I regret to have to inform you that an unfortunate error in our invoice No B 832 of 18th August has just come to light The correct charge for polyester shirts, medium, is £5.30 each and not £5.00 as stated. We are therefore enclosing a debit note for the amount undercharged, namely £6.30.
The mistake is due to a typing error and we are sorry it was not noticed before we sent the invoice.