Please see screenshots, when we have many clients, we may not be able to check so carefully for the notification emails and handle each case in time. Service allocated to customers means we are charged, but client actually haven't paid successfully, this leads us to lose money when we don't even know it. And need to spend manpower to settle it. It does not worth it. For example, client is a debit card, the balance not enough, then simply tell the client reason, ask client to topup and try again, that will be much easier.