In app/controllers/members_controller.rb line 15 change
def login_user_from_api_token
to
def get_user_from_token

It's better to leverage devise & devise-jwt and use the current_user object. In order to get this working in this repo you'll need to update the Gemfile:

gem "devise" gem "devise-jwt"

Then bundle update devise devise-jwt, as I noticed with the gem versions included in this repo there was bug with decoding the token (I assume this is why the custom decode method is used in this repo).

After this you can remove the get_user_from_token method all together since the before_action :authenticate_user! will give you current_user.

For example:

# app/controllers/members_controller.rb
class MembersController < ApplicationController
  before_action :authenticate_user!

  def show
    render json: {
      message: "If you see this, you're in!",
      user: current_user
    }
  end
end