Visa Reason Code 12.7

Required transaction data was missing, malformed, or invalid when the charge was submitted.

A field required by the card network (merchant ID, transaction reference, etc.) was missing or incorrectly formatted on submission.

Almost always a processor/gateway integration issue, not a storefront or customer-facing problem.

Your gateway's submission log showing the data that was actually sent.

Not validating required transaction fields before submission to your payment processor.