php - Integration with ZOHO invoice

Question

I am exploring Zoho-invoice api and trying to integrate with my application. But i am stuck and cant find out what is the reason.

Please help :

This is how i am calling the API :

$fields = array(
                    'contact_name' => urlencode([name]),
                    'billing_address' => array('address' => urlencode([address]), 'city' => urlencode([city]), 'state' => urlencode([state]), 'zip' => urlencode([pincode]), 'country' => urlencode([country])),
                    'contact_person_id' => urlencode([id]),
                    'email' => urlencode([email])
            );
$jsonData = json_encode($fields);

//Initialize connection 
$ch = curl_init("https://invoice.zoho.com/api/v3/contacts?authtoken=[authtoken]&organization_id=[id]&JSONString={$jsonData}"); 
curl_setopt($ch, CURLOPT_VERBOSE, 1);//standard i/o streams 
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);// Turn off the server and peer verification 
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, FALSE); 
curl_setopt($ch, CURLOPT_RETURNTRANSFER, TRUE);//Set to return data to string ($response) 
curl_setopt($ch, CURLOPT_POST, TRUE);//Regular post   

//Execute cUrl session 
$response = curl_exec($ch);
curl_close($ch);

I am sending correct auth-token and organization key.

But I am getting this error response :

 "code":1048,"message":"Sorry, there was an internal error. Please contact support@zohoinvoice.com for assistance."

Any help will be appreciated. Thank you