How to encode a already encoded json data(as string) into another json in swift 4, iOS 11.3, xcode 9?

Question

I am trying to encode a already encoded json data into another json as a string element.

1. First I have created a json data as string with jsonEncoder,

2. Now I have to send that json data(string) as an element of another jsonEncoder's element.

So far I have created this.

my first structs are

struct OrderDetailJSON: Encodable {
    var allOrder: [AllOrder]
    let TaxDetials: TaxDetail

    init(allOrder: [AllOrder] = [AllOrder](), TaxDetials: TaxDetail) {
        self.allOrder = allOrder
        self.TaxDetials = TaxDetials
    }

    mutating func addOrder(orders allOrders: AllOrder){
        allOrder.append(allOrders)
    }

}

struct AllOrder: Encodable {
    let date_time: String
    let item: String
    let name: String
    let price: String
}

struct TaxDetail: Encodable {
    let tax_per: String
    let tax_name: String
}

and I am using json encoder to encode this,

var jsonString = ""
var cartData = [CartDataModel]() `//My data Model`
do {
            let taxex = TaxDetail(tax_per: defaults.string(forKey: "STORE_TAX")!, tax_name: defaults.string(forKey: "STORE_TAX_NAME")!)
            var placeOrder = OrderDetailJSON(TaxDetials: taxex)
            var allOre: AllOrder!
            for item in cartData {
                allOre = AllOrder(date_time: item.time, item: "\(item.quantity)", name: item.name, price: "\(item.price)")
                placeOrder.addOrder(orders: allOre)
            }
            let jsonData = try JSONEncoder().encode(placeOrder)

            jsonString = String(data: jsonData, encoding: .utf8)!
            print(jsonString)
            print(jsonData)

        }catch{
            print("Encode error...")
        }

the json output I am getting is,

{
  "TaxDetials": {
    "tax_per": "5",
    "tax_name": "CGST & SGST"
  },
  "allOrder": [
    {
      "date_time": "NA",
      "name": "Manchurian",
      "item": "2",
      "price": "87"
    },
    {
      "date_time": "NA",
      "name": "Paneer Tikka",
      "item": "3",
      "price": "150"
    },
    {
      "date_time": "NA",
      "name": "snacks",
      "item": "2",
      "price": "54"
    }
  ]
}

Now I have to send this json data as a string element of another json, which is like this

struct OrderPlace: Encodable {
    let apikey: String
    let ord_store_name: String
    let ord_amount: String
    let cust_mob: String
    let store_id: String
    let order_details: String
}

do {
     let orders = OrderPlace(apikey: "382dfc83", ord_store_name: storeName, ord_amount: "\(finalCartPrice)", cust_mob: defaults.getMobNo(), store_id: storeId, order_details: jsonString) 
           orderPlaceUrl.httpBody = try JSONEncoder().encode(orders)
       }catch{
           print("Encode error...")
      }

It's throwing dataCorrupted error. But when I changed the json string from " " to ' ' I am getting the response inside postman.

So, how can I covert above json string (with " ") into below json string (with ' ')

{
  'TaxDetials': {
    'tax_per': '5',
    'tax_name': 'CGST & SGST'
  },
  'allOrder': [
    {
      'date_time': 'NA',
      'name': 'Manchurian',
      'item': '2',
      'price': '87'
    },
    {
      'date_time': 'NA',
      'name': 'Paneer Tikka',
      'item': '3',
      'price': '150'
    },
    {
      'date_time': 'NA',
      'name': 'snacks',
      'item': '2',
      'price': '54'
    }
  ]
}

Note: just comment if anyone need any more information.