protected function prepareJsonPayload(array $data, array $binary_data = [])
{
$payload = ['api_key' => $this->api_key, 'format' => 'json', 'json' => json_encode($data)];
$payload['sig'] = Sailthru_Util::getSignatureHash($payload, $this->secret);
if (!empty($binary_data)) {
$payload = array_merge($payload, $binary_data);
}
return $payload;
}