This field is described in full in section 11, but attention is drawn to the following key sub-fields.
Tag 01 – Item number
In a dual message configuration, this tag must always be present in authorisation related messages, but set to the value 001.
In a single message configuration, the following applies.
Elavon assigns an item number to each approved transaction ‘captured’. These are sales, pre-authorisation completions, ‘force posts’, and refunds.
The item number will increase in value by 1 from 000 to 999 with each approved transaction in a given batch. Once it reaches the maximum value of 999, the batch must be settled resulting in the batch number increasing by 1 and the item number reverting to 000.
The Elavon host will return the item number in sub-field 001 in Field 48 of the appropriate 1110, 1210, 1230 or 1430 response message.
Submitting terminals should supply this value in Field 48 of the next transaction in order to confirm that it received the previous response.
Should the incoming item number be one less than expected, the Elavon host will compare the transaction type, card account number and transaction amount with that of the previously captured item.
If these are the same, the most recent transaction is considered a duplicate and the previously issued approval code will be retrieved and sent back to the terminal
If the comparison finds that the key details are not the same, then the previously captured item will be automatically reversed by the Elavon host, as it will be assumed that the terminal did not receive the previous response.
Any other unexpected incoming item number will result in the transaction being declined by Elavon with the Response Code 131 – Invalid Sequence Number.
Item number ‘000’ should be used by a terminal until the first transaction (eligible for capture) in a new batch is approved, or in authorisation only scenarios.
Tag 05 – Void item number
This sub-field is only required in reversal requests for single message implementations where the Elavon acquiring host captures transactions for settlement.
It is important to emphasise that provided the item number exists in the current batch, it will be reversed by the Elavon host regardless of the contents of other sub-fields and fields.
Details of reversal processing are given in section 6.