ios - PHP adaptive payments -

i'm trying use paypal parallel payments ios app , after found out ios sdk does't support adaptive payments, decided pass data php file , let handle parallel payments me, new php. i've managed create php project, install composer, , used add "paypal/adaptivepayments-sdk-php":"2.*" project. i'm trying use documentation create payments, i'm little lost. here code far :

    <?php  require_once __dir__ . '/vendor/autoload.php';   // sets config file path(if config file used) , registers classloader  // array containing credentials , confiuration parameters. (not required if config file used) // array containing credentials , confiuration parameters. (not required if config file used) $config = array(     'mode' => 'sandbox',     'acct1.username' => 'jb-us-seller_api1.paypal.com',     'acct1.password' => 'wx4wtu3s8my44s7f'     );  $service = new adaptivepaymentsservice($config);  $payrequest = new payrequest(); // add optional params if($_post["feespayer"] != "") {     $payrequest->feespayer = $_post["feespayer"]; }  $response = $service->pay($payrequest); if(strtoupper($response->responseenvelope->ack) == 'success') {     // success } 

it keeps returning following error:

fatal error: uncaught exception 'ppinvalidcredentialexception' message 'invalid userid ' in /users/charlie/phpstormprojects/adaptivepaymentstesting/vendor/paypal/sdk-core-php/lib/ppcredentialmanager.php:120 

anyone have ideas or suggestions?