Remember an overcast is a situation where a customer pays an amount higher and above the real value for goods, due to an error in the total amount calculated in the invoice. The suplier is expected to send a credit note to the customer, noting an error in the invoice and accepting to refund the excess amount to the customer. In the sales day book, the sales account will be debited (because a sale had occur) and a suspense account credited.
A suspense account is an account in the books of an organization in which items are entered temporarily before allocation to the correct or final account.