Lex V2 Test Bot responseCard not showing

Hi, I have created below given Lambda function to display responseCard. Message is displayed but responseCards buttons are not showing on test Bot also on CloudFormation. Please suggest:

export const handler = async (event) => {
    // Create the response
    const response = {
        "sessionState": {
            "intent": {
                "name": "intentName",
                "slots": {
                    "slotName": null
                }
            },
            "dialogAction": {
                "type": "ElicitSlot",
                "slotToElicit": "slotName"
            }
        },
        "messages": [
            {
                "content": "Please select an option",
                "contentType": "PlainText"
            }
        ],
        "responseCard": {
            "version": 1,
            "contentType": "application/vnd.amazonaws.card.generic",
            "genericAttachments": [
                {
                    "title": "Title",
                    "subTitle": "Please select",
                    "imageUrl": null,
                    "buttons": [
                        {
                            "text": "Text 1",
                            "value": "Value 1"
                        }
                    ]
                }
            ]
        }
    };
    return response;
};