active_model_serializers/docs/howto/add_top_level_links.md

How to add top-level links

JsonApi supports a links object to be specified at top-level, that you can specify in the render:

  links_object = {
    href: "http://example.com/api/posts",
    meta: {
      count: 10
    }
  }
  render json: @posts, links: links_object

That's the result:

{
  "data": [
    {
      "type": "posts",
      "id": "1",
      "attributes": {
        "title": "JSON API is awesome!",
        "body": "You should be using JSON API",
        "created": "2015-05-22T14:56:29.000Z",
        "updated": "2015-05-22T14:56:28.000Z"
      }
    }
  ],
  "links": {
    "href": "http://example.com/api/posts",
    "meta": {
      "count": 10
    }
  }
}

This feature is specific to JsonApi, so you have to use the use the JsonApi Adapter