Getting "Sorry, I didn't get any response." message when I tried Hand-off feature

When I tried Multi-surface conversations (Hand-off from Google Home to Android Google Assistant), I'm getting "Sorry, I didn't get any response." I'm using Action SDK and locale is "ja".

Here is my response:

{
    "conversationToken": "(token)",
    "expectUserResponse": true,
    "isInSandbox": true,
    "expectedInputs": [
        {
            "possibleIntents": [
                {
                    "intent": "actions.intent.NEW_SURFACE",
                    "inputValueData": {
                        "@type": "type.googleapis.com/google.actions.v2.NewSurfaceValueSpec",
                        "context": "Sure, I have some sample images for you.",
                        "notificationTitle": "Sample Images",
                        "capabilities": [
                            "actions.capability.SCREEN_OUTPUT"
                        ]
                    }
                }
            ],
            "inputPrompt": {
                "richInitialPrompt": {
                    "items": {
                        "simpleResponse": {
                            "textToSpeech": "PLACEHOLDER_FOR_NEW_SURFACE"
                        }
                    }
                }
            }
        }
    ]
}

Does anyone know why?