When the system reports the Error - TX DUPLICATE message, it is because the customer performs more than one transaction within 5 minutes, with the same card, same amount and to the same merchant.
1. Perform another transaction with a different amount.
2. Wait more than 5 minutes.
In the case of performing these steps and the error still persists. You can write to support at: email@example.com sending us a screenshot and the case.