Mastercard Reason Code 4850

A transaction that should have posted as a credit/refund was processed as a purchase charge instead.

A coding error in your payment integration flipped a refund transaction into a new charge.

A processing bug, not a customer dispute in the usual sense — fix the root cause if you see more than one.

Your system's record of the transaction type actually intended.

Not validating transaction-type coding (credit vs. purchase) in your payment integration.