Payment gateways sometimes return error codes that look confusing. Here is what the common ones mean.
Authentication failed
The gateway could not verify the card. Re-check the card details or contact your bank.
Insufficient funds
The card has no available balance. Top up or use another method.
Card expired
Update your card details or use a different card.
Transaction declined
The bank refused the payment. Contact your bank to find out why.
Gateway unavailable
The payment processor is having an outage. Wait and retry later.
General advice
Retry with a different card if possible. Use store credit if you have a balance. Contact support with the exact error text and invoice number if the problem continues.