attachmentAction2.json

{
  "actions": [
    {
      "id": "1",
      "name": "select_directmessage_participant",
      "text": "Select a user...",
      "type": "select",
      "data_source": "users",
      "confirm": {
        "text": "Are you sure? This action is not reversable",
        "title": "",
        "ok_text": "Okay",
        "dismiss_text": "Cancel"
      },
      "selected_options": [
        {
          "value": "U8JS3A1D0"
        }
      ]
    }
  ],
  "attachment_id": "1",
  "callback_id": "select_directmessage_participant",
  "channel_id": "D8LECLJAK",
  "is_ephemeral": true,
  "message_ts": "1531516498.000003",
  "prompt_app_install": false
}