If a purchase has been declined, it is likely because the available balance on the Card was less than the purchase amount. Merchants do not have access to your Card balance and cannot automatically deduct the available balance for a purchase. So it is important that you inform the merchant the balance of your Card if it is less than the amount of your purchase.
Some merchants, such as restaurants, hotel and car rental reservations require the Card to have an available balance that is 15-20% greater than the purchase amount to ensure there are sufficient funds to pay for the final anticipated amount of the purchase (for tips, service charges, incidental expenses, etc.). This is a standard practice for merchants who accept Visa cards. In all cases, only the actual amount spent will be deducted from the Card.