What is a transaction authentication number (TAN)?

Transaction Authentication Number, TAN, is the authorization number of a transaction notified by the acquiring bank, indicating that an operation has been successfully completed and will be paid to the bank account of the POS. 

TAN number is unique, which means that the combination of numbers can never be duplicated and it consists of 8 to 12 digits. There are acquiring banks that mix numbers and letters to identify the authorization number.

Transaction authentication number can be used to locate any transaction and used in case of dispute between the merchant and the bank as a proof of a payment.