Fraud detection from Banks for "card not present transactions" -- meaning the card information is being typed into a payment system such as MyStudio, Amazon, or any other E-commerce based platform -- are more strict compared to when cards are being physically swiped.
If you are seeing that a perfectly good payment method is getting declined, even though all payment information from customers are correct, the reason could very well be that the customer's credit card company is flagging the transaction as possible fraud.
The above check from the bank is especially true if you are manually entering a payment information in for the customer, and the first payment is due on a future date. In this case, our system will authorize a $0 transaction to ensure that the payment method is valid, so that we can properly charge all future payments.
TO RESOLVE THIS: Simply have the customer call their bank to remove the hold/fraud flag and all should be well going forward.