rich_text_input_basic.json

{
    "type": "rich_text_input",
    "action_id": "action_id",
    "initial_value": {
        "type": "rich_text",
        "elements": [
            {
                "type": "rich_text_section",
                "elements": [
                    {
                        "type": "text",
                        "text": "I'm rich"
                    }
                ]
            }
        ]
    },
    "focus_on_load": false,
    "placeholder": {
        "type": "plain_text",
        "text": "Hello"
    }
}