Receipts creation in OM

Hi Team, I need to know how to mention amount without checking 'prepayment' option in the order management. Is it every time we need to check the "Prepayment" option against the "Check" or "Cash" payment type, if we use these types? What if we don't want to use the "Prepayment" method option and still we want to mention the amount and generate the receipts as per the receipt method? I tried to create the receipt by clicking the first line as "Prepayment" check and mentioned the amount or percent and in the second line I didn't check the "Prepayment" check