This check fires when the same payment details have been used by the same shopper reference in the last 48 hours.
The optional shopperReference field allows merchants to pass a unique user identifier with the transaction. This is usually the unique user ID used to identify the user in the merchant's internal systems. By using this field, this check acts as a velocity check on any particular user on the merchant's site. This is particularly important for account takeovers, which tend to come from registered accounts with otherwise good history.