If Account Funding Transactions (AFTs) are declined but normal purchases with the same card are successful, it could be an issue with the cardholder's bank. The bank may decline an AFT because the related feature is not enabled for that specific card account, often as a security measure.
To resolve this, the cardholder must contact their bank and request that the AFT feature be enabled for their card.
Additionally, AFTs require specific sender or recipient information to be processed successfully. Ensure you are providing the necessary information. See Perform an Account Funding Transaction for more information.