actions_block_checkboxes.json

{
    "type": "actions",
    "block_id": "fake_block_id",
    "elements": [
        {
            "type": "checkboxes",
            "action_id": "actionId-0",
            "options": [
                {
                    "text": {
                        "type": "mrkdwn",
                        "text": "*a*"
                    },
                    "value": "a",
                    "description": {
                        "type": "plain_text",
                        "text": "*a*"
                    }
                },
                {
                    "text": {
                        "type": "mrkdwn",
                        "text": "*b*"
                    },
                    "value": "b",
                    "description": {
                        "type": "plain_text",
                        "text": "*b*"
                    }
                },
                {
                    "text": {
                        "type": "mrkdwn",
                        "text": "*c*"
                    },
                    "value": "c",
                    "description": {
                        "type": "plain_text",
                        "text": "*c*"
                    }
                }
            ]
        }
    ]
}