How can i post a NVPair like a hashmap?

[AaronXu]

I have a script need to post the params like below, someone can help me to resolve this issue? thanks in advance!
{
  "subject": "test subject",
  "body": "test body",
  "amount": "1",
  "order_no": "ETyeh35145223663",
  "channel": "upacp_pc",
  "currency": "cny",
  "client_ip": "127.0.0.1",
  "app": {
    "id": "app_e9KKKC5uLSSKSuX1"
  },
  "extra":{
    "result_url":"https://pingxx.com/?as=12|d=2"
  },
  "time_expire":"",
  "description": "test1description",
  "metadata":[  
    {  
      "01":[1,2],
      "02": "组的key和value的长度总和"
    }
  ]
}