> For the complete documentation index, see [llms.txt](https://docs.payments.thalescloud.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.payments.thalescloud.io/nfc-payment/implement-nfc-payment/make-payment/optional-features.md).

# Optional features

### Overview

Use these implementation details to complete the payment flow.

Use these features only when they are supported by your payment experience.

### SDK

#### Display the authentication timer

Use `DeviceAuthenticationTimeoutCallback` to show the remaining time before the end user must tap again.

Register the callback with `registerDeviceAuthTimeoutCallback()` when the payment flow reaches `onReadyToTap()`.

This callback is useful for payment experiences that require a second tap, such as manual mode.

{% tabs %}
{% tab title="Android Java" %}

```java
ContactlessTransactionListener paymentCallback = new ContactlessTransactionListener() {

    @Override
    public void onReadyToTap() {
        // ...
        // Register the timeout callback to update the end user on the
        // remaining time before the second tap.
        D1PayConfigParams.getInstance()
            .getContactlessTransactionListener()
            .registerDeviceAuthTimeoutCallback(
                new DeviceAuthenticationTimeoutCallback() {
                    @Override
                    public void onTimer(int remain) {
                        // Update the countdown screen with the current
                        // remaining time.
                    }

                    @Override
                    public void onTimeout() {
                        // Inform the end user that authentication timed out.
                    }
                }
        );

        // Inform the end user to tap again and show the countdown screen
        // for the CDCVM validity period.
    }

    // ...
};
```

{% endtab %}
{% endtabs %}

#### Display transaction details

To improve the end user experience, the issuer application can display transaction details, such as amount, currency, and transaction type, when `TransactionData` is available.

Use the `TransactionData` object to access these values.

The callback that exposes `TransactionData` depends on the payment experience. For example, in manual mode, `TransactionData` is only available in `onTransactionCompleted()`.

{% tabs %}
{% tab title="Android Java" %}

```java
ContactlessTransactionListener paymentCallback = D1PayConfigParams.getInstance()
                                                                  .getContactlessTransactionListener();
TransactionData transaction = paymentCallback.getTransactionData();
```

{% endtab %}
{% endtabs %}

#### Enable or disable contactless payment

You can disable contactless payment by default and enable it only after the end user signs in and selects **Pay** in the issuer application.

After the D1 SDK initializes, call `D1PayWallet.setContactlessTransactionAllowed(false)`.

When the end user selects **Pay**, call `D1PayWallet.setContactlessTransactionAllowed(true)` to enable the contactless transaction.

{% hint style="warning" %}
Enable contactless payment for each transaction, then disable it again after the transaction completes or is canceled.
{% endhint %}


---

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