Sequence number of the transaction.
This field is user definable and can be used at the users discretion. When submitting any type of transaction for approval, this sequence number may be any numeric value 0 to 2400. This is a purely optional field for the Host Capture SettlementMode, and you may choose to send a unique number or simply send every transaction with zeros. The host will echo the sequence number submitted from the authorization request back in the SequenceNumber field.
However, if you are processing with the Terminal Capture SettlementMode, SequenceNumber CANNOT remain zero, and must contain a number that is incremented for each transaction you authorized. When it reaches 2400, the SequenceNumber should then start over at 1 again.