If a customer is checking out after entering all required fields and select Complete Order the order (with the exception of Square Integrated systems either complete a pre-authorization or completes a charge, this is based on the POS Integration.
At that time if they receive a decline message or error there is an issue with either the funds on their account or the information that they have entered associated with the credit card. These orders do not get finalized and will not appear on OrderCloud.
Some banks will grab these attempts and hold the funds even though the card was not approved. These attempts will be removed from the customers accounts based on the practices of the card issuing bank.