An SDK that fits your existing stack

TerminalSdk.getReady(
    configuration = TerminalSdk.Configuration(
        pinPadConfiguration = pinPadConfiguration,
    ),
    endpoint = IntegrationEndpoint,
    // Your app manages these credentials; keep the secret protected, never in plain code.
    authorizationGrant = ClientCredentialsGrant(
        scope = "<oauth2scope>",
        clientId = "<oauth2clientid>",
        clientSecret = "<oauth2clientsecret>",
    ),
    onGetReadyCompleted = { result ->
        when (result) {
            is GetReadySucceeded -> // terminal is Ready
            is GetReadyFailed -> // inspect result.cause
        }
    },
)

TerminalSdk.INSTANCE.getReady(
    new TerminalSdk.Configuration(pinPadConfiguration),
    IntegrationEndpoint.INSTANCE,
    new ClientCredentialsGrant(
        "<oauth2scope>",
        "<oauth2clientid>",
        "<oauth2clientsecret>"
    ),
    result -> {
        // GetReadySucceeded or GetReadyFailed
        return Unit.INSTANCE;
    }
);

TerminalSdk.startTransaction(
    merchantId = UUID.fromString("1fd50a7b-4eed-4bf4-ba9a-13a2ac353987"),
    emvConfiguration = readEmvConfiguration(),
    transactionParameters = TransactionParameters(
        amount = 1250,
        currency = "GBP",
    ),
    onUiMessage = { uiMessage -> render(uiMessage) },
    onTransactionIdSet = { transactionId -> store(transactionId) },
    onTransactionResult = { result ->
        // TransactionCompleted does not mean approved —
        // check result.processingResult for the authorisation outcome
    },
)

TerminalSdk.INSTANCE.startTransaction(
    UUID.fromString("1fd50a7b-4eed-4bf4-ba9a-13a2ac353987"),
    readEmvConfiguration(),
    new TransactionParameters(1250, "GBP"),
    uiMessage -> { render(uiMessage); return Unit.INSTANCE; },
    transactionId -> { store(transactionId); return Unit.INSTANCE; },
    result -> {
        // TransactionCompleted does not mean approved —
        // check result.getProcessingResult()
        return Unit.INSTANCE;
    }
);