How to get Distance? using api.openrouteservice.org/optimization

results :
i got perfect results but missing Distance

{
  "summary": {
    "cost": 20474,
    "unassigned": 0,
    "delivery": [
      6
    ],
    "amount": [
      6
    ],
    "pickup": [
      0
    ],
    "service": 1800,
    "duration": 20474,
    "waiting_time": 0,
    "computing_times": {
      "loading": 200,
      "solving": 1
    }
  }
}