Can't see nested elemets in API call

Thanks.

In tag’s schema.json, there’s no relation yet, as I was not able to add in Strapi admin due to error.

{
  "kind": "collectionType",
  "collectionName": "tags",
  "info": {
    "singularName": "tag",
    "pluralName": "tags",
    "displayName": "Tag",
    "description": ""
  },
  "options": {
    "draftAndPublish": true
  },
  "pluginOptions": {},
  "attributes": {
    "name": {
      "type": "string",
      "required": true
    }
  }
}