We apologize for the inconvenience. We will work with mastercard and our bank partner to resolve this issue. Please note most card transactions fails due to payment gateways or banks supporting the payment gateways. We did not believe this in beginning; however, when I moved to the other side (providing cards) , we realized the same.

Please send an email to support@karboncard.com with the following details.

1. Merchant name of transaction

2. Date/time of transaction

3. Email of card holder 

4. Type of card

5. Error screenshot

We would reach out to our Mastercard support and try our best to resolve this issue ASAP.