List SMS topics

curl -X GET 'https://www.unitpost.com/api/v1/sms/topics' \
  -H 'Authorization: Bearer YOUR_API_KEY' \
  -H 'User-Agent: my-app/1.0'

{
  "object": "list",
  "has_more": false,
  "data": [
    {
      "object": "topic",
      "id": "id_123",
      "name": "Example",
      "description": "string",
      "channel": "email",
      "default_opt_in": false,
      "created_at": "2026-01-01T00:00:00.000Z",
      "updated_at": "2026-01-01T00:00:00.000Z"
    }
  ]
}