How to Access Magento Rest API in iOS swift 4

I am write code to post data from Magento REST API for IOS Application put get me error. I try from login and register view controller in the same code get me the same error The api Magento REST API . I success to get data from api but error to post data in api

    self.internetConnectionChecker { (status) in
    if status{
    KVNProgress.show();
    let userLoginApi = "http://3.85.198.62/4apps/rest/V1/integration/customer/token"
                    let parameters: Parameters = ["username": username, "password": password]
                    let header : HTTPHeaders = ["Content-Type": "application/json"]
                    Alamofire.request(userLoginApi, method: .post, parameters: parameters,  headers: header).responseObject {  (response: DataResponse<User>) in
                        KVNProgress.dismiss()
                         print(response.request?.url)
                        print(response.request?.allHTTPHeaderFields)
                        let json = try! JSONSerialization.jsonObject(with: response.data!, options: JSONSerialization.ReadingOptions.mutableContainers)
                        print(json)
                            DispatchQueue.main.async {
                                loginCallback(response.result.value!)}
                            self.maincontroller.SuccessMessage(title: "تسجيل الدخول", successbody: "")

The Output 
{
    message = "Decoding error: \nUnable to unserialize value. Error: Syntax error\n#0 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Webapi/Rest/Request/Deserializer/Json.php(64): Magento\\Framework\\Serialize\\Serializer\\Json->unserialize('password=Abc%40...')\n#1 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Webapi/Rest/Request.php(141): Magento\\Framework\\Webapi\\Rest\\Request\\Deserializer\\Json->deserialize('password=Abc%40...')\n#2 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Webapi/Rest/Request.php(199): Magento\\Framework\\Webapi\\Rest\\Request->getBodyParams()\n#3 /opt/bitnami/apache2/htdocs/4apps/app/code/Magento/Webapi/Controller/Rest/InputParamsResolver.php(97): Magento\\Framework\\Webapi\\Rest\\Request->getRequestData()\n#4 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Interception/Interceptor.php(58): Magento\\Webapi\\Controller\\Rest\\InputParamsResolver->resolve()\n#5 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Interception/Interceptor.php(138): Magento\\Webapi\\Controller\\Rest\\InputParamsResolver\\Interceptor->___callParent('resolve', Array)\n#6 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Interception/Interceptor.php(153): Magento\\Webapi\\Controller\\Rest\\InputParamsResolver\\Interceptor->Magento\\Framework\\Interception\\{closure}()\n#7 /opt/bitnami/apache2/htdocs/4apps/generated/code/Magento/Webapi/Controller/Rest/InputParamsResolver/Interceptor.php(26): Magento\\Webapi\\Controller\\Rest\\InputParamsResolver\\Interceptor->___callPlugins('resolve', Array, Array)\n#8 /opt/bitnami/apache2/htdocs/4apps/app/code/Magento/Webapi/Controller/Rest/SynchronousRequestProcessor.php(85): Magento\\Webapi\\Controller\\Rest\\InputParamsResolver\\Interceptor->resolve()\n#9 /opt/bitnami/apache2/htdocs/4apps/app/code/Magento/Webapi/Controller/Rest.php(188): Magento\\Webapi\\Controller\\Rest\\SynchronousRequestProcessor->process(Object(Magento\\Framework\\Webapi\\Rest\\Request\\Proxy))\n#10 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Interception/Interceptor.php(58): Magento\\Webapi\\Controller\\Rest->dispatch(Object(Magento\\Framework\\App\\Request\\Http))\n#11 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Interception/Interceptor.php(138): Magento\\Webapi\\Controller\\Rest\\Interceptor->___callParent('dispatch', Array)\n#12 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/Interception/Interceptor.php(153): Magento\\Webapi\\Controller\\Rest\\Interceptor->Magento\\Framework\\Interception\\{closure}(Object(Magento\\Framework\\App\\Request\\Http))\n#13 /opt/bitnami/apache2/htdocs/4apps/generated/code/Magento/Webapi/Controller/Rest/Interceptor.php(26): Magento\\Webapi\\Controller\\Rest\\Interceptor->___callPlugins('dispatch', Array, Array)\n#14 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/App/Http.php(137): Magento\\Webapi\\Controller\\Rest\\Interceptor->dispatch(Object(Magento\\Framework\\App\\Request\\Http))\n#15 /opt/bitnami/apache2/htdocs/4apps/generated/code/Magento/Framework/App/Http/Interceptor.php(24): Magento\\Framework\\App\\Http->launch()\n#16 /opt/bitnami/apache2/htdocs/4apps/lib/internal/Magento/Framework/App/Bootstrap.php(261): Magento\\Framework\\App\\Http\\Interceptor->launch()\n#17 /opt/bitnami/apache2/htdocs/4apps/index.php(39): Magento\\Framework\\App\\Bootstrap->run(Object(Magento\\Framework\\App\\Http\\Interceptor))\n#18 {main}";
    trace = "<null>";
}

The error you see has happened on the Magento side Decoding error: \nUnable to unserialize value... It points to the problem unserializing JSON params. So I've tried to play with encoding on the Alamofire request and URLEncoding.queryString works for me. Here is my code

Alamofire.request(userLoginApi, method: .post, parameters: parameters, encoding: URLEncoding.queryString, headers: header).responseData {  (response: DataResponse<Data>) in
    let json = try! JSONSerialization.jsonObject(with: response.data!, options: JSONSerialization.ReadingOptions.mutableContainers)
    print("json", json)
}