Where should I add ActionDispatch middleware for a Rails API which includes both Web views and API

Question

I have an application which uses a React component to update the user profile. With a backend of Rails, I'm attempting to pass a flash message on the #update action which is connected to the Rails API that I built for the React frontend. ActionController::API doesn't have the middleware of ActionController::Base and I can't figure out where to include the ActionDispatch middleware for the ActionController::API.

I've tried adding it as a module (hoping that it may already be within the application):

Controller

class Api::V1::BaseController < ActionController::API
    include ActionDispatch::Flash

I've also tried including the middleware into the config/application.rb

config/application.rb

module Subs
  class Application < Rails::Application
    config.generators do |generate|
          generate.assets false
          generate.helper false
          generate.test_framework  :test_unit, fixture: false
        end
    # Initialize configuration defaults for originally generated Rails version.
    config.load_defaults 5.2

    config.middleware.use ActionDispatch::Flash
  end
end

I imagine that adding it to a general config/application.rb is redundant as the ActionDispatch::Flash is already included in the application.

Where could I add a middleware specifically for the ActionController::API ? Or how could I give it access to the ActionDispatch::Flash that is already present in the ActionController::Base?