curl --request GET \
  --url https://api.x.com/2/account_activity/webhooks/{webhook_id}/subscriptions/all/list \
  --header 'Authorization: Bearer <token>'

{
  "data": {
    "application_id": "<string>",
    "subscriptions": [
      {
        "user_id": "<string>"
      }
    ],
    "webhook_id": "<string>",
    "webhook_url": "<string>"
  },
  "errors": [
    {
      "title": "<string>",
      "type": "<string>",
      "detail": "<string>",
      "status": 123
    }
  ]
}