Serializing an array of resources

The documentation shows a clear example on how to do it for one resource:

post = Post.find(1)
JSONAPI::ResourceSerializer.new(PostResource).serialize_to_hash(PostResource.new(post, nil))

But how does one serialize an array of resources?

For example, suppose this is my controller:

class ProductsController < ApplicationController
  def index
    @products = Product.where(visible: true)
    render json: JSONAPI::ResourceSerializer.new(ProductResource).serialize_to_hash(ProductResource.new(@products, nil))
  end
  def show
    product = Product.find(params[:id])
    render json: JSONAPI::ResourceSerializer.new(Admin::ProductResource).serialize_to_hash(ProductResource.new(product, nil))
  end
end

GET /products/2
The show method returns 1 resource in JSON API compliant format. Even better, I could remove the entire show method and it will still work because the inherited methods do something similar.

GET /products/
However, the index method returns a 500 error. Removing the index method entirely would partially solve the problem, I get an array back containing ALL products. But what if I need it to return only the active=true products? For that I need an array serializer no?

Suggestions?
Am I missing something?
Is the documentation incomplete?
Have I perhaps not understood how to work with JSON API? I've got the impression the idea is to not add any logic to your controllers at all and let the URLs do all the work?

Start with the serializer example in the linked documentation and compare it with the ProductsController index action using Product.where(visible: true). Verify how arrays of ProductResource objects are intended to be serialized, then clarify the documentation for the filtered collection case; done means the array workflow is unambiguous.