OAuth2 returns invalid_client error

good day, I'm having trouble with getting the access token. I've followed the guide here: http://developers.box.com/oauth/ and already get my client_id, client_secret, and set the redirect_uri on the App settings (OAuth2 parameters) section. Here is the code for the file client.php ``` <?php $client_id = 'my_client_id_here'; //removed $post_url = 'https://www.box.com/api/oauth2/authorize'; include 'includes/header.php'; ?> <div id="content"> <form action="<?php echo $post_url; ?>" type="POST" enctype="application/x-www-form-urlencoded"> <input type="text" name="response_type" value="code"> <input type="text" name="client_id" value="<?php echo $client_id; ?>"> <input type="text" name="state" value="vexhax97td8xf_SomeTemporaryValueForTesting"> <input type="submit"> </form> <div id="response"></div> </div> <?php include 'includes/footer.php'; ?> ``` and here's code for the file something.php (this is where the redirect_uri will go) ``` <?php $client_id = 'my_client_id_here'; //removed $client_secret = 'my_client_secrect_here'; //removed $post_url = 'https://www.box.com/api/oauth2/token'; $code = $_GET['code']; include 'includes/header.php'; $fields_params = array( "grant_type" => 'authorization_code', "code" => $code, "client_id" => $client_id, "client_secret" => $client_secret ); $ch = curl_init(); curl_setopt($ch, CURLOPT_URL, $post_url); curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1); curl_setopt($ch, CURLOPT_POST, true); curl_setopt($ch, CURLOPT_POSTFIELDS, $fields_params); curl_setopt($ch, CURLOPT_HTTPHEADER, array( 'Content-Type: application/json', 'Accept: application/json' )); $data = curl_exec($ch); curl_close($ch); $json = json_decode($data, true); var_dump($json); ?> <div id="content"> <?php //Nothing fancy, just for displaying passed values if (isset($_GET)) var_dump($_GET); if (isset($_POST)) var_dump($_POST); ?> </div> <?php include 'includes/footer.php'; ?> ``` ...now what happens is, 1.) on the first step (client.php), there is a form there with submit button. 2.) After i clicked on the submit button, i get redirected to the Box' login page with the button "Authorize". 3.) after entering login details and allow granting access for my app. I now gets redirected to the redirect_uri that i've set on the App settings (something.php), where in this file, it will execute curl post to get an access token, but i get stuck at this part, the curl result returns with the error: ``` array(2) { ["error"]=> string(14) "invalid_client" ["error_description"]=> string(34) "The client credentials are invalid" } ``` I'm sure that I have entered my client_id and client_secret correctly which I've obtained from the App settings. And the url for the redirect_uri, is also SSL enabled. Any solutions, ideas why this is happening? Thank you for your help.