Sequence number of this transaction.
This field contains a terminal-generated transaction sequence number to be submitted in all authorization request messages. This number is echoed back to the terminal in the TransactionNumber for the purpose of assisting in the matching of authorization request and response messages. This value must be in the range 0001 to 9999 and should be incremented on each authorization request message. This number should automatically increment from 9999 to 1. 0 is an invalid transaction number.