public function create_credential_legacy($recipient_name, $recipient_email, $achievement_name, $issued_on = null, $expired_on = null, $course_name = null, $course_description = null, $course_link = null, $custom_attributes = null){

        $data = array(
            "credential" => array(
                "group_name" => $achievement_name,
                "recipient" => array(
                    "name" => $recipient_name,
                    "email" => $recipient_email
                ),
                "issued_on" => $issued_on,
                "expired_on" => $expired_on,
                "custom_attributes" => $custom_attributes,
                "name" => $course_name,
                "description" => $course_description,
                "course_link" => $course_link
            )
        );

        $client = new \GuzzleHttp\Client();

        $params = array('Authorization' => 'Token token="'.$this->getAPIKey().'"');

        $response = $client->post($this->api_endpoint.'credentials', array(
            'headers' => $params,
            'json' => $data
        ));

        $result = json_decode($response->getBody());

        return $result;
    }