Handling Failures

links: Face Liveness Lite

When a liveness check fails, the SDK returns a LivenessLiteEvent.Failure event. This event contains a type parameter, a CafFailureType enum that tells you exactly why the process was unsuccessful.

Understanding and handling the type parameter is critical for providing clear, actionable feedback to your users so they can correct the issue and try again.

The Failure Model

The SDK delivers failures through the LivenessLiteEvent sealed interface. Both capture-level and recognition-level failures are reported as LivenessLiteEvent.Failure, ensuring you can always access the type and description.

LivenessLiteEvent.kt

public sealed interface LivenessLiteEvent {

    /**
     * Liveness failure event with specific failure type.
     *
     * @param response The signed response from the server
     * @param type The specific type of failure that occurred
     * @param description User-friendly description of the failure
     */
    public data class Failure(
        val response: String,
        val type: CafFailureType,
        val description: String
    ) : LivenessLiteEvent
}

Ensure the JWT response is evaluated on the backend. This process must include validating the token's signature and verifying the isAlive and isMatch fields. Do not perform these validations on the client side.

Using the type Parameter

The type parameter returns a CafFailureType enum constant (e.g., TOO_DARK or FACE_TOO_FAR).

Best Practice: Do not display the raw enum name or the description directly to your end-users. Instead, intercept the type and map it to a user-friendly, localized message in your app's UI to guide them on how to fix the problem.

Available Failure Types

If the image capture is successful but the engine fails to authenticate or process the face, the SDK returns a LivenessLiteEvent.Failure.

Below is the list of possible CafFailureType values returned during this phase:

Type	Description
UNKNOWN	Generic failure
TOO_MUCH_MOVEMENT	Excessive head motion
TOO_BRIGHT	Over-illumination
TOO_DARK	Low light conditions
MISALIGNED_FACE	Face alignment failure
FACE_TOO_FAR	Face too distant
FACE_TOO_CLOSE	Face too close
SUNGLASSES	Eye-obscuring eyewear
OBSCURED_FACE	Partial face obstruction
EYES_CLOSED	Closed eyes during capture
MULTIPLE_FACES	Multiple faces detected
BACKGROUND_ISSUE	Unsuitable background
DEVICE_ISSUE	Incompatible device
EYEWEAR	Eyewear detected
FACE_NOT_FOUND	Face detection failure
FRAMES_BLURRY	Blurry frames detected
MOTION_ISSUE	Device motion error
LIGHTING_ISSUES	Poor lighting conditions
REJECTED	Transaction rejected
SYSTEM_ERROR	Internal system error
TIMEOUT	Session timeout
USER_NOT_FOUND	User lookup failure
DEVICE_RESTART	Device state error
PROCESSING_FAULT	Processing error
FACE_AUTHENTICATION	Face authentication failed

Example Implementation

Here is an example of how you might handle a LivenessLiteEvent.Failure and map the type parameter to helpful user guidance:

Kotlin

fun handleLivenessFailure(failure: LivenessLiteEvent.Failure) {
    // 1. The signed server payload is available if needed
    println("Server response: ${failure.response}")

    // 2. Map the 'type' to a user-friendly message
    val userMessage = when (failure.type) {
        CafFailureType.TOO_DARK -> "It's a bit too dark. Please move to a brighter room."
        CafFailureType.FACE_TOO_FAR -> "Please bring the phone closer to your face."
        CafFailureType.EYES_CLOSED -> "Please keep your eyes open and look directly at the camera."
        CafFailureType.MULTIPLE_FACES -> "Ensure you are the only one in the frame."
        CafFailureType.TIMEOUT -> "Time ran out. Please try again when you are ready."
        CafFailureType.REJECTED,
        CafFailureType.FACE_AUTHENTICATION -> "We couldn't verify your face. Please try again."
        //...
        else -> "An unexpected error occurred (${failure.type}). Please try again."
    }

    // 3. Display the message in your UI
    showErrorDialog(userMessage)
}

Java

public void handleLivenessFailure(LivenessLiteEvent.Failure failure) {
    // 1. The signed server payload is available if needed
    System.out.println("Server response: " + failure.getResponse());

    // 2. Map the 'type' to a user-friendly message
    String userMessage;

    switch (failure.getType()) {
        case TOO_DARK:
            userMessage = "It's a bit too dark. Please move to a brighter room.";
            break;
        case FACE_TOO_FAR:
            userMessage = "Please bring the phone closer to your face.";
            break;
        case EYES_CLOSED:
            userMessage = "Please keep your eyes open and look directly at the camera.";
            break;
        case MULTIPLE_FACES:
            userMessage = "Ensure you are the only one in the frame.";
            break;
        case TIMEOUT:
            userMessage = "Time ran out. Please try again when you are ready.";
            break;
        case REJECTED:
        case FACE_AUTHENTICATION:
            userMessage = "We couldn't verify your face. Please try again.";
            break;
        //...
        default:
            userMessage = "An unexpected error occurred (" + failure.getType() + "). Please try again.";
            break;
    }

    // 3. Display the message in your UI
    showErrorDialog(userMessage);
}

Links:

Face Liveness LiteHandling FailuresUi CustomizationChangelog