Reason code · Mastercard
Mastercard 4840: fraudulent processing of transactions
4840 is a legacy Mastercard fraud code that doesn’t appear in the current Chargeback Guide. Fraud claims now run as 4837 and a few chip-specific codes. If you see 4840, read the notice’s description and ask your processor which current rule applies.
What 4840 means
4840 is a legacy Mastercard code, historically labeled Fraudulent Processing of Transactions. The old label points to a fraud complaint about how a charge was processed.
Here’s the catch. 4840 doesn’t appear anywhere in Mastercard’s current Chargeback Guide. Today Mastercard handles fraud through four codes: 4837 No Cardholder Authorization, 4870 and 4871 for chip fraud, and 4849 Questionable Merchant Activity. Even Stripe’s reason-code table lists 4840 without a real description.
Why old codes still show up
Mastercard has been folding its long list of reason codes into a few consolidated ones. Its Guide still lets banks send several retired numbers for now, such as 4812, 4831, 4841, 4846, 4855, 4859 and 4860, while warning they will eventually be eliminated. 4840 is further along: it’s gone from the Guide entirely. Processor systems and older merchant guides still carry it.
What the customer told their bank
You can’t tell from the number alone. Read the description on your notice and any cardholder statement attached to it. Then ask your processor which current reason the bank is using. That’s the rule your response has to meet.
Time limit
There’s no current rule text for 4840, so there’s no network time limit to quote. Go by the due date on your notice. If the case turns out to be a 4837 fraud claim, the bank had 120 days from the transaction to file it, and your own window is the shorter one your processor sets.
What proof matters
Once you know the real claim, answer that. For fraud claims, that means proof tying the real cardholder to the purchase: who bought, how they were verified, and where the goods or service went.
The common mistake
Researching an old code’s rules and answering those. Rules written for a retired code won’t match what the bank is checking now. Answer the claim on the notice, under the rule your processor confirms.
Dispute Daddy builds this for you
Dispute Daddy reads the notice, keeps the due date in view and builds the response from your own records for you to approve. See how the method works.
