download_zip api

function dropbox_download_zip($folder_path, $file_name)
{
    $ch = curl_init();
    curl_setopt($ch, CURLOPT_URL, 'https://content.dropboxapi.com/2/files/download_zip');
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);
    curl_setopt($ch, CURLOPT_POST, 1);

    $headers = array();
    $headers[] = "Authorization: Bearer " . DROPBOX_TOKEN . "";
    $headers[] = "Dropbox-API-Arg: {\"path\": \"$folder_path\"}";
    $headers[] = "Content-Type: application/octet-stream; charset=utf-8";
    $headers[] = "User-Agent: api-explorer-client";
    $headers[] = "Content-Length: 0";
    curl_setopt($ch, CURLOPT_HTTPHEADER, $headers);
    $result = curl_exec($ch);
    if (curl_errno($ch)) {
        echo 'Error:' . curl_error($ch);
    } else {
        $zip_file_name = $file_name . '.zip';

        header('Content-type: application/zip');
        header('Content-Disposition: attachment; filename=' . $zip_file_name);
        header('Content-Length: ' . strlen($result));
        echo $result;


        die();
    }
}

I have this code but for large files (eg 300mb) there is an error 'allowed memory size of bytes exhausted', I think it is due to the large file size,
please tell me how you can make curl result immediately written to zip file