Swift Invalid value around character 0 - php

Question

i need help with my app login code.
I try to make a Http Request to my local server, a simple login request with mail and password but i've a issue and i don't know how to fix it.
#IBAction func clickConnexionBtn(sender: AnyObject)
{
if(!mailTf.text!.isEmpty && !passwordTf.text!.isEmpty)
{
let mail = mailTf.text!
let password = passwordTf.text!
let param = String(format: "mail=%#&password=%#", arguments: [mail, password]);
let url = NSURL(string: "http://localhost:8888/MoneyManager/login.php")!
RequestObject.sharedInstance.prepareRequest(param, _url: url, _method: "POST")
let task = NSURLSession.sharedSession().dataTaskWithRequest(RequestObject.sharedInstance.request)
{ data, response, error in
if error != nil
{
let alertView = UIAlertController(title: "Error server", message: "Could not connect to server", preferredStyle: UIAlertControllerStyle.Alert)
self.showViewController(alertView, sender: self)
}
else
{
let serverResponse = NSString(data: data!, encoding: NSUTF8StringEncoding)
print("Server response: \(serverResponse)")
do
{
if let json = try NSJSONSerialization.JSONObjectWithData(data!, options: .AllowFragments) as? NSDictionary {
print(json)
}
} catch let error2 as NSError {
print(error2.description)
}
}
}
task.resume()
}
}
So this is the action when i click on the 'connexionButton'.
Unfortunately when i try to Serialize the JSON, i have this error:
Error Domain=NSCocoaErrorDomain Code=3840 "Invalid value around character 0." UserInfo={NSDebugDescription=Invalid value around character 0.}
My PHP code is like:
if($result)
{
$return = array("Success" => 1, "Message" => "Insert user done", "user_id" => $_SESSION['id'], "api_key" => $_SESSION['api_key']);
echo json_encode($return);
}
Here is the code of my 'print("Server ....")'
Server response: Optional(Connexion successfully {"Success":1,"Message":"Insert user done","user_id":"9","api_key":"aa3b0c16fc63efe207be1a7471ac234a"})
Its all the data that i want to get and turn into JSON object
I look many subject but no one of them could help me cause most of the people use Alamofire to perform request.
So please if you have an idea, i listening
Thanks all.