Fast array of messages with afnetworking

I want to post some array of numbers along with other parameters, but I am getting the error

{ error = "The operation couldn\U2019t be completed. (Cocoa error 3840.)"; }

Here is what I am trying, in my api controller I have

func postRequest(url: String, params: NSDictionary, callback:(NSDictionary) -> ()) {

    manager.responseSerializer.acceptableContentTypes = NSSet(array: ["text/plain", "text/html", "application/json"]) as Set<NSObject>

    manager.POST(url, parameters: params,
    success: { (operation: AFHTTPRequestOperation!,responseObject: AnyObject!) in
        //println("JSON: " + responseObject.description)
        callback(responseObject as! NSDictionary)
    },
    failure: { (operation: AFHTTPRequestOperation!,error: NSError!) in
        //println("Error: " + error.localizedDescription)
        callback(["error" : error.localizedDescription])
    })
}

      

        
        
        
      

    

Then, in my opinion, the controller, I am sending a message with

    var contacts = ["xxxxxxxx", "xxxxxxxx", "xxxxxxxx"]
    var params = ["id" : 1, "contacts" :  contacts ]
    api.postRequest(Constants.ApiUrl.Friends, params: params, callback: { (response) -> () in
        //self.didReceiveResponse(response)
        println(response)
    })

      

        
        
        
      

    

Please how can I make this message work