send fax using curl

First of all, is there any reason you don't want to use our SDKs? Using our SDKs is the most convenient way to access RingCentral platform and call the APIs. What programming language do you use? https://github.com/ringcentral

If you still want to write from scratch using curl, see the example from the API explorer https://developer.ringcentral.com/api-reference#Fax-sendFaxMessage

+ Phong

My code is working properly on localhost but it is not working on server.
Here is my code:- Credentials are dummy 
/////////////////////////////////////////////////////////////////////////////////////
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, "https://platform.devtest.ringcentral.com/restapi/oauth/token");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, "username=+15450345789&password=2145854#&extension=101&grant_type=password");
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_USERPWD, "kukadkashjasd" . ":" . "f9ReaNa3TSe1RYx8hS-8jahdkjdsjhadhjkjahds");

$headers = array();
$headers[] = "Accept: application/json";
$headers[] = "Content-Type: application/x-www-form-urlencoded";
curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);

$result = curl_exec($ch);

$result = json_decode($result);
if (curl_errno($ch)) {
   echo 'Error:' . curl_error($ch);
}
  $token = $result->access_token;
curl_close($ch);
$ch = curl_init();   

            $url = "https://platform.devtest.ringcentral.com/restapi/v1.0/account/~/extension/~/fax";
            curl_setopt($ch, CURLOPT_URL, $url);
            curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
            curl_setopt($ch, CURLOPT_POSTFIELDS, array(
        'username'      => '+15450345789',
        'password'      => "2145854",
        'to'     => '+9874563210',
        'from'=>'+142452454565',
        'attachment'    => '@' . realpath('/var/www/html/pdf2-199167_doc.pdf'),
        'coverpagetext' => 'PHP FaxOut Via cURL'
    ));
            $dataarray =array(
                              'accept: application/json',
                              'authorization: Bearer '.$token
                              );
            curl_setopt($ch, CURLOPT_HTTPHEADER, $dataarray);

            $response = curl_exec($ch);
            curl_close($ch);
            $data = (json_decode($response));
            echo '<pre>';
print_r($data); exit;
/////////////////////////////////////////////////////////////////////////////////////////////
It is working perfect on my local server. But when I upload it to server,
I am getting this error:-

    [errorCode] => InvalidContent
    [message] => Either filename or content type should be specified, attachment [1]: []
    [errors] => Array
        (
            [0] => stdClass Object
                (
                    [errorCode] => MSG-356
                    [message] => Either filename or content type should be specified, attachment [1]: []
                    [attachmentFileName] => 
                    [attachmentNumber] => 1
                )

        )

    [attachmentFileName] => 
    [attachmentNumber] => 1
)

Sir could you please send me complete code step by step to send fax with attachment using RingCentral SDK in php?