I've noticed that event hough I sent "False" the same credit card with same amount on the same date can be charged twice or more. Like that Key doesn't make any effect.
Express duplicate checking monitors the most recent 25 transactions in the current batch. We look for a match on the following: Credit card number, transaction amount, transaction type.
Based on your report, it's possible that the duplicate transaction was processed more than 25 transactions apart; or, that the transactions were processed as different types (Credit and Debit). If you have a specific example you feel we should investigate, please e-mail the details to Certification2@fisglobal.com.
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