This service is specific to debit card transactions. If you wish to OPT IN, your debit card purchases will bring your account negative with the standard $25 fee per transaction. In order to choose this option, you must be approved for Overdraft Courtesy Pay and have an available limit to overdraw your account. If you have chosen to set up overdraft protection, those transfers will take affect before bringing the account negative.
To avoid going negative with your debit card transactions, you can choose to OPT OUT which will deny your debit card purchases if there is not enough money in your checking account to cover the charge.