Callbacks and Notifications

Callbacks and Notifications

The EPAS wrappers are not just request or response APIs. A large part of the public surface is callback-driven. This page complements the integration guide by listing the callback families and what they mean.

Core Operational Callbacks

These callbacks are part of the normal transaction lifecycle.

Callback	Purpose
Display	Show cashier-facing text from the terminal.
Print receipt	Receive structured merchant and cardholder receipts.
Print report	Receive report output as plain text.
Verify signature	Ask whether the cashier accepts the signature.
Handle voice referral	Collect an approval code during voice referral.
Payment code required	Collect a payment code from cashier or operator.
VAT amount required	Collect VAT or sales tax amount when the terminal requires it.
Loyalty card presented	Decide how to handle a presented loyalty card.
Check DCC on original transaction	Confirm whether a prior transaction used DCC.
Parameter download available	Permit or defer a terminal parameter update.
Log	Receive wrapper and terminal log messages.

Status and Notification Callbacks

These callbacks keep the ECR UI and diagnostics aligned with the terminal state.

Notification	Purpose
Link status	Connection up or down between ECR and terminal.
Busy status	Long-running terminal work such as download or service state.
Card action	Card inserted or removed.
Card accepted	Card accepted by terminal, often with masked PAN details.
Raw message	Raw EPAS message received for support or diagnostics use.

Swift Delegate Shape

The Swift wrapper uses EpasClientDelegate on the main actor.

UI and printing

swift
func display(text: String)
func printReceipt(receipt: ReceiptData)
func printReport(report: String)
func log(level: LogLevel, text: String)

Cashier decision callbacks

swift
func verifySignature(displayText: String) async -> BooleanCallbackResult?
func forceFallback(displayText: String) async -> BooleanCallbackResult?
func handleVoiceReferral(displayText: String) async -> TextCallbackResult?
func paymentCodeRequired(displayText: String) async -> TextCallbackResult?
func vatAmountRequired(displayText: String) async -> DecimalCallbackResult?
func loyaltyCardPresented(cardNumber: String) async -> BooleanCallbackResult?
func checkDccOnOriginalTransaction(displayText: String) async -> BooleanCallbackResult?
func parameterDownloadAvailable(displayText: String) async -> Bool

Terminal status and diagnostics

swift
func linkStatusChanged(isConnected: Bool)
func busyStatusChanged(isBusy: Bool)
func cardStatusChanged(isInserted: Bool)
func epasMessageReceived(message: String)

Design Notes

• Callback handlers should return quickly.
• UI prompts should be marshalled to the correct UI thread or actor.
• Even after an abort request, final receipts and responses may still arrive.
• Receipt callbacks may happen more than once per transaction.
• Raw-message callbacks should normally be enabled only in diagnostics or support scenarios.

For behavioural examples, see Client Callbacks.