public function purchase($email, array $items, $incomplete = null, $message_id = null, array $options = [])
{
$data = $options;
$data['email'] = $email;
$data['items'] = $items;
if (!is_null($incomplete)) {
$data['incomplete'] = (int) $incomplete;
}
if (!is_null($message_id)) {
$data['message_id'] = $message_id;
}
return $this->apiPost('purchase', $data);
}