References and Identifiers

Merchant References

First Data allows additional transaction references for the following transaction types:

  • Payment
  • Payment with Gratuity
  • Recurring Payment
  • Refund

Message elements InitiatorTransactionIdentification (Tx/InitrTxId) and MerchantReferenceData (Tx/MrchntRefData) may be optionally used by merchants to pass additional references to the Central Acceptance Platform. The table below shows the usage of these two optional fields within different interfaces in Fiserv.

Reference elementDescriptionSupported format in FiservNEXO Acquirer fieldNEXO Retailer field
Merchant Reference 1Reference number provided by merchant that will be passed to acquirer, issuer (if supported by scheme) and printed on cardholder receipt. It could be generated by the Merchant POS or manually entered on the POI.15 ANTx/InitrTxIdStatementReference
Merchant Reference 2Reference number provided by merchant generated by the Merchant POS or manually entered on the POI. Used by merchants for their own internal purposes. The reference will only be available on Fiserv internal systems.

Internal reservation number, booking number/reference
30 ANTx/MrchntRefDataSaleToAcquirerData


Transaction identifiers

Order ID

IPG assigns an order ID to transactions in the response message element Tx/RcptTxId. The value must be used in related transactions such as incremental authorizations and completions. The request tag Tx/OrgnlTx/RcptTxId is not supported in Payment messages.

Transaction ID

This element uniquely identifies a transaction. It must be unique for each message pair (request, response). A technical void (or cancel) can use the same transaction ID.

The transaction ID consists of two sub-fields: TxDtTm and TxRef.

The TxDtTm is used as the transaction time. In an online transaction it must be close to the current time otherwise it is possible that authorization system won't accept the transaction.

TxRef is forwarded to some end-systems. To avoid problems the following rules should be met:

TxRef should be a numeric counter with values in [000000, 999999].
If transaction n follows transaction n-1, then TxRef in n must be greater than the one in n-1.
If transaction n-1 has a TxRef > 900000, It is possible to use a value less then 100000 for transaction n. This is to allow a restart of the counter, when all values are used.
It is also a good idea not to increment the counter by 1, but by a higher number (e.g.: 10). The reason for this is the following: It is possible to configure an automatic cut-over in IPG for a terminal (or store). In this case IPG must send a message to the next system. This message requires also a TxRef (or more exact a trace number which is derived from TxRef). IPG will use the last value of TxRef + 1. If after this the terminal sends this TxRef again, it will fail (this may depend on the ensystem IPG uses to forward the transaction).

Store, merchant and terminal identifiers

Every request message sent by the POI must include two merchant identifiers: Store ID and Merchant ID. The Store ID is an IPG identifier of the "shop" entity, while the Merchant ID is the Acquirer card brand specific merchant identifier that will be sent in authorization and clearing messages. The POI will include the Store ID in element Envt/POI/GrpId and the Merchant ID in element Envt/Mrchnt/Id/Id.

Every terminal gets assigned an Acquirer identifier (referred to as Acquirer TID) and a Fiserv identifier (referred to as External TID). This section describes the relation between the two and the way they are reflected in the nexo Acquirer protocol. The term "Acquirer" is used throughout the document with a wider meaning than the industry standard meaning of "Acquiring Bank/Processor". It could also refer to different payment providers including alternative payment providers (APMs).

There are 2 basic modes of operation for Fiserv integrated devices:

  • Acquirer Processor
  • PSP

When Fiserv drives a terminal as an acquirer processor, the External TID will also be used as an Acquirer TID, being sent to card schemes and printed on receipts.

When Fiserv drives a terminal as a PSP, it typically routes the traffic to one or more Acquirers (or APMs). The merchant and acquirer will identify a terminal by its Acquirer assigned TID, while the External TID will only be known by Fiserv systems and not forwarded to card schemes.

Terminal numbering

  1. In Germany productive TIDs are centrally assigned by Deutsche Kreditwirtschaft (DK).
    For the integration via Fiserv, TIDs have to be in the range 54xxxxxx and
    have to be requested from our German business department.
  2. For other countries the format limitation is less strict. In general a limitation to 8
    characters/digit should be sufficient
  3. TIDs (or TID ranges) will be provided from your Fiserv contact.
  4. On request, Fiserv can also use terminal IDs defined by terminal providers.

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