There are several potential reasons:

1. A problem with the credit card/Debit Card;
   
2. Your online Payment Gateway settings
   
3. Incorrect card details provided during payment.

Here are some things to try:

1. Make sure that your debit/credit card details are correct when making a purchase;
   
2. Contact your debit/credit card provider with the error message, they may be able to identify the issue you are having.
   
3. If you are still having transaction problems, please contact us with details of the error message.