number_cruncher_consumer.rb

# app/controllers/calculation.rb
def create
  req = ActiveSupport::JSON.decode(request.body)
  
  calculator = StatefulCalculator.new
  
  # to_crunch => [[1, 2, 3], [9, 10, 11]]
  
  @sums = req["to_crunch"].map do |nums|
    NumberCruncher.new(calculator).crunch(nums)
  end
    
  render :calculation_view
end

replace the req[“to_crunch”] with req[“arrays_to_crunch”] because in the blog it's explained as req[“arrays_to_crunch”]