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 app/serializers/fullcalender_engine/event_serializer.rb
In fullcalendar_engine.gemspec: