Most probably this error happened because the cardholder (your client) did not have enough money in his card's account to proceed/deduct the purchase/order.
In this article you will be going to know about:
How to investigate the reason that caused this error?
You can check the "Response Code" in the transaction from your PayTabs's dashboard. Also, to check the used card's last 4 digits, you can check the description attribute under the "Payment Method" tab, and the "Customer Details" for the customer information.
Reason #1: Not have enough money on the used card on the payment page.
This means that the funds/money available on the cardholder's account is less than the order/purchase amount. In this case, you will need to inform your clients to retry using a card that contains enough money to complete the purchase/order.