Most of the them, when working on Rails with ActiveModel::Serializer you will do something like this:
render json: user, serializer: UserSerializer
Or if it's a list
render json: users, each_serializer: UserSerializer
This way, Rails will take care of calling your serializer with the item or calling each item on the list with the serializer.
What happens if you want to manually call them inside a list? You can do
render json: ActiveModel::Serializer::CollectionSerializer.new(
This way you will tell
ActiveModel::Serializer to call your serializer
UserSerializer for a collection of items and use
users as the data, so the gem will iterate the list of users and serialize them.