radio_button_group_basic.json

{
    "type": "radio_buttons",
    "action_id": "radio_buttons",
    "options": [
        {
            "text": {
                "type": "plain_text",
                "text": "A"
            },
            "value": "A"
        },
        {
            "text": {
                "type": "plain_text",
                "text": "B"
            },
            "value": "B"
        },
        {
            "text": {
                "type": "plain_text",
                "text": "C"
            },
            "value": "C"
        }
    ],
    "initial_option": {
        "text": {
            "type": "plain_text",
            "text": "A"
        },
        "value": "A"
    }
}