Use ActiveModel Serializer for json response.

[kuldeepaggarwal]

In app/serializers/fullcalender_engine/event_serializer.rb

module FullcalendarEngine
  require 'active_model_serializers'
  class EventSerializer < ActiveModel::Serializer
    attributes :id, :title, :description, :start, :end, :allDay, :recurring

    def description
      object.description || ''
    end

    def start
      object.starttime.iso8601
    end

    def end
      object.endtime.iso8601
    end

    def allDay
      object.all_day
    end

    def recurring
      object.event_series_id?
    end
  end
end

In fullcalendar_engine.gemspec:

s.add_dependency "active_model_serializers", ">= 0.9.4"