public function create($file, $purpose, array $headers = [])
{
$response = $this->getClient()->request('POST', 'v1/files', ['headers' => $headers, 'multipart' => [['name' => 'purpose', 'contents' => $purpose], ['name' => 'file', 'contents' => fopen($file, 'r')]]]);
return json_decode($response->getBody(), true);
}