External Host Interface (EHI)

The External Host Interface (EHI) offers a way to exchange transactional data between the Thredd processing system and the Program Manager’s externally-hosted systems. All transaction data processed by Thredd is transferred to the external host system via EHI in real time. EHI provides two main functions:

Real-time Transactional Data Feed

Thredd receives global real-time card and payment-related notifications from the card schemes (Visa and Mastercard networks). These notifications are merged into a single Thredd message format which your systems can process. The real-time notifications are sent via a secure VPN connection to the external host URL endpoint you have requested for your programme. These include notifications for: Authorisations, Presentments, Load and Balance Transfers and Expired Cards. For details see Transaction Types.

Your systems should respond with an acknowledgement of receipt of the message.

The EHI data feed can be used to ensure you can provide your cardholders with real-time information.



In addition to the real-time data feed, Thredd also provides daily batch XML reports, via sFTP. You can use this data to support your payment reconciliations. See the Transaction XML Reporting Guide.

Payment Authorisation Control

The payment authorisation process is initiated when a cardholder makes a purchase with a merchant, who then seeks authorisation for the card payment via their acquirer. See the figure below.

EHI payment authorisation flow

EHI payment authorisation flow

When a payment authorisation request is received from the card schemes, Thredd first performs conventional transaction-related card and cardholder checks, such as EMV data, PIN, CVV2, velocity checks, fraud checks and card product checks.
Your EHI Operating Mode will determine whether Thredd or your systems manage the payment authorisation. For example:

  • Gateway Processing (Mode 1) (where your systems maintain the card balance) - you make the authorisation decision and respond to Thredd to indicate whether the transaction can be approved or declined.
  • Cooperative Processing (Mode 2) (where Thredd maintains the card balance) - Thredd approve or decline and sends to you; you can overrule any approved decision.
  • Full Service Processing (Mode 3) (where Thredd maintains the card balance) - Thredd makes the authorisation and provides you with the response.
  • Gateway Processing with STIP (Mode 4) and Gateway Processing with STIP (Mode 5) (where your systems maintain the card balance) - you perform authorisation.

Thredd provides Stand-In authorisation if your system is unavailable.
Thredd provides other flexible mode options, where a combination of Thredd and external host authorisation can be used. For more information, see EHI Operating Modes.
Thredd will process your response and respond to the card scheme (Mastercard or Visa). The authorisation decision process is in real time.

Transaction Types

Below are a list of transaction types supported on the Thredd system and reported via EHI.

AuthorisationA request message to approve or decline a payment authorisation. Authorisation type transactions includes normal authorisation requests and authorisation reversal from MasterCard/Visa.This type of message is a request to reserve a specified amount on the card to cover a later financial message which is expected to follow.
FinancialA notification message which Thredd generates based on the batch clearing files received from the card schemes. Financial type transactions include: First Presentment, Financial Reversal, Second Presentment, Chargeback, Chargeback Reversal and Fees.
LoadA notification that the customer’s card balance has been credited (via a Web Service or Smart Client).
UnloadA notification that the customer’s card balance has been debited (via a Web Service or Smart Client).
PaymentA notification of a payment originating from a non-card network entity (for example, faster payment or direct debit), paying funds into or out of the customer's card.

Note: This is only relevant to customers using the Thredd Banking-enabled card functionality.
Balance AdjustmentA notification that the customer’s balance has been updated (via a Web Service or Smart Client). This can be either a credit or debit.
Card ExpiryA notification that the customer’s card has expired. Thredd generates this based on the expiry date configured for the card.



For more information on EHI, refer to the EHI Guide.