American Express Reason Code C14

The cardmember paid for the same purchase through another payment method as well.

The customer paid by cash, another card, or another channel for the same order, in addition to this charge.

Reconciling across payment channels is the defense — if a double-payment occurred, refund it directly.

Order and payment records showing only one valid payment was collected, or proof of the alternate payment.

Not reconciling orders across payment channels before this dispute arises.