code: private function download(AbstractRequestTransport $requestTransport, $filename)
      {
          $response = $this->apiTransport->send(
              $requestTransport->getPath(),
              $requestTransport->getMethod(),
              $requestTransport->getQueryParams(),
              $requestTransport->getBody(),
              $requestTransport->getHeaders()
          );
  
          if ($response->getStatusCode() === 200) {
              return (new Psr7\Response())
                  ->withHeader('Content-Type', 'text/csv; charset=utf-8')
                  ->withHeader('Content-Disposition', 'attachment; filename="' . $filename . '"')
                  ->withBody($response->getBody());
          }
  
          return $response;
      }
docs: @param AbstractRequestTransport $requestTransport
  @param string                   $filename
  
  @return Psr7\MessageTrait
  
  @throws TransportException