I'm writing a tiny Sinatra application (Facebook Messenger bot), so I'm using
map '/webhook' do
rackup -p 5000
/chatbot/config.ru:5:in `block in <main>': undefined method `include' for #<Rack::Builder:0x007feb32926e70> (NoMethodError)
Content of config.ru file is handled by Rack::Builder, not by Ruby itself. Specificaly the include line is evaluated in context of Rack::Builder and that gives you the undefined method. According to the rest of the code, you dont need to include it as you use full path to the inner Module/Class
If you realy need to include it, do so in separete (ruby) file and require that file in config.ru.