Mastercard Reason Code 4840: Fraudulent Processing

What Mastercard reason code 4840 means

4840 is a legacy fraud code with a specific shape: the cardholder did do business with you, once. Their complaint is that you then processed one or more further transactions on the same card that they never agreed to. Classic examples are a server running a card twice at the end of a tab, or a merchant reusing card details saved from a previous purchase.

Mastercard now handles this claim within 4837 No Cardholder Authorization, but some processors and reports still show 4840. Because it alleges deliberate misuse, a pattern of 4840s can draw scrutiny from your acquirer beyond the individual disputes.

4840 vs a duplicate charge

The distinction matters for your response:

Common causes

• One-click post-purchase upsells where the customer didn’t realize accepting the offer created a second charge
• Saved cards charged for a reorder or add-on without a clear confirmation step
• Bar and restaurant tabs where the card was swiped for a pre-authorization and again at close
• Recurring billing set up from a one-time purchase without explicit consent
• In rare cases, an employee deliberately running cards

Evidence that wins a 4840 dispute

1. Separate order records for each charge: distinct order numbers, items, timestamps and confirmation emails.
2. Authorization data for each transaction: approval codes, plus chip, PIN or 3-D Secure results where present.
3. Proof of consent for the additional charge: the upsell acceptance click with timestamp and IP, a signed tab, or the checkout page showing the add-on and its price.
4. Delivery or fulfillment for each order separately.
5. Communication in which the customer acknowledges the second purchase.

Show the issuer that the “extra” transaction had its own customer action behind it. Without that link, the claim stands.

How to prevent 4840 chargebacks

• Make upsell acceptance an explicit step that shows the additional amount, and send a separate confirmation for it.
• Require a confirmation step before charging a stored card for any new purchase.
• Close bar and restaurant tabs against the original pre-authorization rather than running the card again.
• Monitor for multiple same-day charges on one card and review them before settlement.
• Restrict staff access to stored card data and keep audit logs.

Should you fight or accept?

Fight when every disputed charge has its own order, its own customer action and its own fulfillment record. Those cases are winnable, although the burden is on you to make the separation obvious.

Accept when the extra charge was a mistake or you can’t show the customer agreed to it. Refund it, and if 4840s are clustering around a particular flow or location, fix that flow first. Fraud-type disputes generally count toward your chargeback ratio whatever the outcome.