download_zip api

I don't have a sample of calling /2/files/download_zip in PHP in particular to share. The documentation has an example of calling it using command line curl though. Likewise, the API v2 Explorer can build sample code for it in a few formats. You can use those as a reference to write your code on your platform using whatever HTTPS client you're using.

the problem is that in the example it works, and I often get allowed memory size of bytes exhausted. I need some good sdk

We don't have an official PHP SDK for Dropbox API v2, but another option is to use a third party library. We have some listed here:

https://www.dropbox.com/developers/documentation/communitysdks

I don't know which, if any, of those happen to implement /2/files/download_zip though.

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

I can't really help with memory management on your system or with configuring third party clients as they're not made by Dropbox. That said, if you want to use curl to save to a local file on your server's local filesytem, you may want to use the 'CURLOPT_FILE' option.