Error trying to post JSON data using Alamofire

I cannot figure out how to send this data to server. I can't find out what's wrong in my code.

This the api documentation:

.

I sent it in postman as form:

This my JSON I sent with my request:

 {  
   "return_data":{  
      "telephone":"0123456789",
      "date_ordered":"2018-11-26 10:58:51",
      "model":"طوق نجاة",
      "order_id":"130",
      "lastname":"fares",
      "firstname":"fares1",
      "product":"130",
      "quantity":"1",
      "opened":"0",
      "comment":"",
      "email":"fareselsokary456@gmail.com",
      "return_reason_id":"2"
   }
}

And this is my code. It sent the request but it gets an error from the server:

func PostReturnReasons(firstName : String, lastName : String, phone : String, email : String,order_id : String,date_orderd : String,product : String,model : String,quantity : String,return_reason_id : String,opened : String,comment : String, complition : @escaping COMplitionHandler){

let body : [String : Any] = [
            "firstname" : firstName,
            "lastname" : lastName,
            "email" : email,
            "telephone" : phone,
            "order_id" : order_id,
            "date_ordered" : date_orderd,
            "product" : product,
            "model" : model,
            "quantity" : quantity,
            "return_reason_id" : return_reason_id,
            "opened" : opened,
            "comment" : comment
    ]

    Alamofire.request("http://brook1.com/api/productreturn/key/12345", method: .post, parameters: ["return_data" : body], encoding: JSONEncoding.default).responseString { (response) in
        print(NSString(data: (response.request?.httpBody)!, encoding: String.Encoding.utf8.rawValue)!)

        if response.result.error == nil{
            let json = try! JSON(data: response.data!)
            print(json)

            complition(true)
        }else{
            complition(false)
            debugPrint(response.result.error as Any)
        }
    }
}