Dropbox nested files download using CURL

Hi Support,

I am downloading files using below function where I am able to download only root files. I am facing issue in downloading files under folder

function dbx_get_file($token, $in_filepath, $out_filepath)
{


$out_fp = fopen($out_filepath, 'w+');

if ($out_fp === FALSE)
{
echo "fopen error; can't open $out_filepath\n";
return (NULL);
}
$url = 'https://content.dropboxapi.com/2/files/download';
$header_array = array(
'Authorization: Bearer ' . $token,
'Content-Type:',
'Dropbox-API-Arg: {"path":"' . $in_filepath . '"}'
);
$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_POST, TRUE);
curl_setopt($ch, CURLOPT_HTTPHEADER, $header_array);
curl_setopt($ch, CURLOPT_FILE, $out_fp);
$metadata = null;
curl_setopt($ch, CURLOPT_HEADERFUNCTION, function ($ch, $header) use (&$metadata)
{
$prefix = 'dropbox-api-result:';
if (strtolower(substr($header, 0, strlen($prefix))) === $prefix)
{
$metadata = json_decode(substr($header, strlen($prefix)), true);
}
return strlen($header);
}
);
$output = curl_exec($ch);
if ($output === FALSE)
{
echo "curl error: " . curl_error($ch);
}
curl_close($ch);
 
fclose($out_fp);
return($metadata);

} // dbx_get_file()
if(isset($_GET['download']))
{
$file = $_GET['download'];
$metadata = dbx_get_file("token", '/'.$file, $file); 

In above code when file under folder is passing for example 'test/abc.png' then it shows error in fopen() + unable to open file/folder.

Please help me to resolve this issue asap