Setting up Absinthe on Phoenix + Bandit project

I am trying to set up Absinthe following the documentation here: Plug and Phoenix Setup — absinthe v1.11.0

on a brand new Phoenix 1.7 project.

I have generated the project with:

mix phx.new api --no-assets --no-ecto --no-dashboard --no-mailer --no-html --no-live --no-gettext --module=API 

and now I try to add Absinthe. I installed dependencies:

  defp deps do
    [
      {:phoenix, "~> 1.7.20"},
      {:telemetry_metrics, "~> 1.0"},
      {:telemetry_poller, "~> 1.0"},
      {:jason, "~> 1.2"},
      {:dns_cluster, "~> 0.1.1"},
      {:bandit, "~> 1.5"},
      {:absinthe_plug, "~> 1.5"}
    ]
  end

And I configured my router:

defmodule APIWeb.Router do
  use APIWeb, :router

  forward "/api/graphql", Absinthe.Plug,
    schema: API.Schema

  forward "/api/graphiql",
    Absinthe.Plug.GraphiQL,
    schema: API.Schema,
    interface: :simple
end

The app compiles but when I make requests to either /api/graphq or /api/graphiql I am getting:

[info] GET /api/graphiql                                                                                                                                                       
[error] ** (Plug.Conn.NotSentError) a response was neither set nor sent from the connection
    (bandit 1.6.7) lib/bandit/pipeline.ex:172: Bandit.Pipeline.commit_response!/1
    (bandit 1.6.7) lib/bandit/pipeline.ex:44: Bandit.Pipeline.run/4                  
    (bandit 1.6.7) lib/bandit/http1/handler.ex:12: Bandit.HTTP1.Handler.handle_data/3                                                                                          
    (bandit 1.6.7) lib/bandit/delegating_handler.ex:18: Bandit.DelegatingHandler.handle_data/3   
    (bandit 1.6.7) lib/bandit/delegating_handler.ex:8: Bandit.DelegatingHandler.handle_continue/2
    (stdlib 6.0.1) gen_server.erl:2163: :gen_server.try_handle_continue/3
    (stdlib 6.0.1) gen_server.erl:2072: :gen_server.loop/7                          
    (stdlib 6.0.1) proc_lib.erl:329: :proc_lib.init_p_do_apply/3

My schema so far is also generated from documentation:

defmodule API.Schema do
  use Absinthe.Schema

  @desc "An item"
  object :item do
    field(:id, :id)
    field(:name, :string)
  end

  # Example data
  @items %{
    "foo" => %{id: "foo", name: "Foo"},
    "bar" => %{id: "bar", name: "Bar"}
  }

  query do
    field :item, :item do
      arg(:id, non_null(:id))

      resolve(fn %{id: item_id}, _ ->
        {:ok, @items[item_id]}
      end)
    end
  end
end

Anyone knows what I’m doing wrong?