Some credit and debit cards have an additional security feature, such as Visa’s 3-D Secure or Mastercard’s SecureCode. In these cases, the card's issuing bank requires additional information to verify it’s the cardholder using the card. MySudo does not control how the bank handles this security measure; the issuing bank does.
In some cases, your bank may send you an SMS or call you with a code. In other cases, no interaction will be required if you are using MySudo from a location the bank considers low-risk for your account.
Using a VPN can sometimes trigger these security features. You may need to try a different egress location or disconnect the VPN while adding your funding source.