Overdrafting is generally not allowed with your Credit Karma Money Spend account and transactions that exceed your available balance will be declined in most cases. Certain types of transactions, such as purchases like certain gas stations, may authorize your account for a different amount than the final transaction amount and can cause a negative balance on your account.
While there are not fees for having your Credit Karma Money Spend account, you will not be able to make transactions or withdrawals from your account until it has a positive balance. Please make sure to resolve any negative balance by making a deposit as soon as you can.