External Host Interface Integration Guide
8. EHI Message Identification Guidance
Your system may receive different types of EHI messages depending on the transaction lifecycle event.
Your system should identify the message type using the EHI fields included in the forwarded payload, especially MTID, Txn_Type, Txn_Stat_Code, CutOffId, and related lifecycle identifiers.
EHI notifications include authorizations, presentments, financial messages, and other payment-related messages. Response behavior depends on the message type.
8.1 Main message categories
| Message category | Common identifiers | Purpose | Expected action from your system |
|---|---|---|---|
| Authorization | MTID=0100, Txn_Type=A | Request for a real-time authorization decision. | Validate the request, evaluate balance and business rules, and return approve, decline, or partial approval when applicable. |
| Authorization repeat | Usually same authorization context with retry or repeat indicators, such as SendingAttemptCount. | Repeated delivery of an authorization message. | Check whether the original message was already processed. Do not apply duplicate balance or ledger impact. Return the same logical response when applicable. |
| Authorization advice | Advice-style authorization message. | Notification related to an authorization event. | Process for transaction history, balance handling, or reconciliation according to your internal rules. |
| Authorization reversal | MTID=0400 or MTID=0420, commonly with Txn_Type=D. | Reversal or adjustment of a previous authorization impact. | Match to the original authorization and release or adjust the related blocked amount. |
| Financial / presentment | Financial notification or first presentment message. | Notification that a transaction is being financially presented or posted. | Match to the original authorization when possible, post or reconcile the transaction, and acknowledge receipt. |
| Financial reversal | Financial reversal message. | Reversal of a previous financial/presentment impact. | Match to the previous financial message and reverse or adjust the prior posted impact. |
| Chargeback | Chargeback notification. | Dispute-related financial event. | Process according to your dispute, ledger, and reconciliation rules. |
| Chargeback reversal | Chargeback reversal notification. | Reversal of a previous chargeback impact. | Match to the original chargeback and reverse or adjust the dispute-related impact. |
| Cut-off | CutOffId present. | Summary-style cut-off message for reconciliation and acknowledgement tracking. | Process the cut-off message, detect duplicates using CutOffId, and return Cut_OffResult. |
8.2 How to identify messages
Your system should use the EHI fields to determine how to process each message.
| Field | How your system should use it |
|---|---|
MTID | Identifies the high-level message type. |
Txn_Type | Identifies the transaction category or lifecycle event. |
Txn_Stat_Code | Provides transaction status context when present. |
Txn_ID / TXn_ID | Identifies the transaction message and supports duplicate detection. |
traceid_lifecycle | Helps link related lifecycle messages. |
Traceid_Message | Identifies the specific message instance. |
Traceid_Original | References the original message, when present. |
Trans_link | Supports transaction linking and matching. |
Auth_Code_DE38 | Useful for matching later messages to the original authorization. |
Ret_Ref_No_DE37 | Retrieval reference number used for matching and investigation. |
CutOffId | Identifies cut-off messages and supports cut-off duplicate detection. |
Message Identification
Identify the message type, then apply the correct processing path
Use EHI fields
MTID, Txn_Type, Txn_Stat_Code, CutOffId, and related lifecycle identifiers.
Identify the message type
Your system should use the EHI fields to determine how to process each message.
Apply the correct processing path
Your system should first identify the message type and then apply the correct processing path.
8.3 Processing expectations
Your system should not treat every EHI message as a new authorization.
Instead, your system should first identify the message type and then apply the correct processing path.
- Decisional message – Return the required authorization decision within the processing window.
- Non-decisional message – Acknowledge receipt and process the message for transaction history, ledger updates, or reconciliation.
- Reversal message – Match the reversal to the original transaction and release, reverse, or adjust the previous transaction impact.
- Financial or presentment message – Match the message to the related authorization when possible and post or reconcile the final transaction.
- Duplicate or retry message – Return the same logical response as the original processing and avoid duplicate balance, block/reserve, or ledger impact.
- Cut-off message – Process the cut-off summary and return
Cut_OffResult.
Important note
Important note: Your system should apply the EHI message type logic using the payload fields exactly as received. The detailed transaction-specific sections that follow explain how each message type should be handled, matched, and answered.
Next steps
Continue to Authorization-Related Messages.