```ruby
require 'ruote'
require 'httpi'

module ScriptoriaCore
  class HttpParticipant < Ruote::StorageParticipant
    def on_workitem
      re_dispatch(in: '60s') unless request_callback
      super
    end

    def on_cancel
      ScriptoriaCore.logger.info "on_cancel: #{workitem.inspect}"
      super
    end

    def request_callback
      sc_workitem = ScriptoriaCore::Workitem.from_ruote_workitem(workitem)

      ScriptoriaCore.logger.info "Making request to `#{sc_workitem.callback_url}' for `#{sc_workitem.participant_name}'"

      request = HTTPI::Request.new
      request.url  = sc_workitem.callback_url
      request.body = sc_workitem.callback_payload.to_json
      begin
        response = HTTPI.post(request)
        if response.code >= 200 && response.code < 300
          ScriptoriaCore.logger.info "Successful response received"
          true
        else
          ScriptoriaCore.logger.info "Error response received"
          false
        end
      rescue Exception => e
        ScriptoriaCore.logger.info "Exception occured: #{e.inspect}"
        false
      end
    end
  end
end
```

Set the content type on the callback request
user
```ruby
require 'ruote'
require 'httpi'

module ScriptoriaCore
  class HttpParticipant < Ruote::StorageParticipant
    def on_workitem
      re_dispatch(in: '60s') unless request_callback
      super
    end

    def on_cancel
      ScriptoriaCore.logger.info "on_cancel: #{workitem.inspect}"
      super
    end

    def request_callback
      sc_workitem = ScriptoriaCore::Workitem.from_ruote_workitem(workitem)

      ScriptoriaCore.logger.info "Making request to `#{sc_workitem.callback_url}' for `#{sc_workitem.participant_name}'"

      request = HTTPI::Request.new
      request.url     = sc_workitem.callback_url
      request.body    = sc_workitem.callback_payload.to_json
      request.headers = {
        "Content-Type" => "application/json"
      }
      begin
        response = HTTPI.post(request)
        if response.code >= 200 && response.code < 300
          ScriptoriaCore.logger.info "Successful response received"
          true
        else
          ScriptoriaCore.logger.info "Error response received"
          false
        end
      rescue Exception => e
        ScriptoriaCore.logger.info "Exception occured: #{e.inspect}"
        false
      end
    end
  end
end
```
assistant